JP3772753B2 - Method for producing carbon nanotube and catalyst composition - Google Patents
Method for producing carbon nanotube and catalyst composition Download PDFInfo
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- JP3772753B2 JP3772753B2 JP2002031935A JP2002031935A JP3772753B2 JP 3772753 B2 JP3772753 B2 JP 3772753B2 JP 2002031935 A JP2002031935 A JP 2002031935A JP 2002031935 A JP2002031935 A JP 2002031935A JP 3772753 B2 JP3772753 B2 JP 3772753B2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 59
- 239000003054 catalyst Substances 0.000 title claims description 35
- 239000002041 carbon nanotube Substances 0.000 title claims description 33
- 229910021393 carbon nanotube Inorganic materials 0.000 title claims description 33
- 239000000203 mixture Substances 0.000 title claims description 13
- 238000004519 manufacturing process Methods 0.000 title claims description 11
- 229910052751 metal Inorganic materials 0.000 claims description 78
- 239000002184 metal Substances 0.000 claims description 78
- 150000001875 compounds Chemical class 0.000 claims description 16
- 229910052799 carbon Inorganic materials 0.000 claims description 15
- 238000006243 chemical reaction Methods 0.000 claims description 13
- 229910052723 transition metal Inorganic materials 0.000 claims description 12
- 150000003624 transition metals Chemical class 0.000 claims description 12
- 239000013078 crystal Substances 0.000 claims description 10
- 238000010304 firing Methods 0.000 claims description 9
- 230000001590 oxidative effect Effects 0.000 claims description 6
- 239000002994 raw material Substances 0.000 claims description 3
- 230000003197 catalytic effect Effects 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 23
- 238000000034 method Methods 0.000 description 22
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 21
- 239000002121 nanofiber Substances 0.000 description 16
- 239000010453 quartz Substances 0.000 description 16
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 16
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 15
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- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 8
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- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical group [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 6
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
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- 229910003481 amorphous carbon Inorganic materials 0.000 description 3
- 238000001241 arc-discharge method Methods 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 239000002079 double walled nanotube Substances 0.000 description 3
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- 239000011261 inert gas Substances 0.000 description 3
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- 229910052750 molybdenum Inorganic materials 0.000 description 3
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- IKHGUXGNUITLKF-XPULMUKRSA-N acetaldehyde Chemical compound [14CH]([14CH3])=O IKHGUXGNUITLKF-XPULMUKRSA-N 0.000 description 1
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- 125000004429 atom Chemical group 0.000 description 1
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- 239000012159 carrier gas Substances 0.000 description 1
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- 229910052746 lanthanum Inorganic materials 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は、高い表面積、高い弾性ヤング率、高い引っ張り強さ及び高い導電性を有するカーボンナノチューブの製造方法に関する。本発明によれば、10nm未満の細いカーボンナノチューブが得られる。
【０００２】
【従来の技術】
カーボンナノチューブは、グラファイトの１枚面を巻いて筒状にした形状を有しており、一層に巻いたものを単層カーボンナノチューブ、多層に巻いたものを多層カーボンナノチューブという。
【０００３】
カーボンナノチューブを製造する方法としては、アーク放電法及び化学蒸着法（ＣＶＤ）による方法が知られている。アーク放電法は、真空中又は不活性気体雰囲気中で炭素棒を電極とし、高電圧・高電流のアーク放電を行い、カーボンナノチューブを製造するものであり、カーボンナノチューブは陰極堆積物中にグラファイト、カーボンナノパーティクルなどと一緒に得られる。ＣＶＤによる方法は、鉄、ニッケルなどの金属微粒子の存在下で原料ガスを数百度で反応させて、カーボンナノチューブを製造するものである。この場合、原料ガスとしては、ベンゼン、トルエン、オルトメチルジアリルケトン、アセチレン、エチレン、メタン等が用いられる。アーク放電法により作られたカーボンナノチューブは、グラファイト層の欠陥の少ないナノチューブが得られるが、アモルファスカーボンなどの不純物が多い。ＣＶＤ法では、不純物が少なく、しかも安価にカーボンナノチューブを製造できるが、生成したカーボンナノチューブはグラファイト層に欠陥が多く、２９００℃程度の熱処理をしないと、欠陥の少ないグラファイト層が形成されないものがほとんどである。
【０００４】
それを、解決する手段として、篠原らはＹ型ゼオライトにコバルトとバナジウムを担持させた触媒を用いて、欠陥の少ない多層カーボンナノチューブが製造できることを報告している(Chemical Physics Letters 303(1999) 117-124)。
【０００５】
本発明者らは、更に結晶性メタロシリケートゼオライトに金属触媒を担持させることにより更に結晶性の良い多層カーボンナノチューブ、単層カーボンナノチューブを得ることが出来ることを見出した。この原因は、シリケート骨格中に存在する金属と担持した金属触媒の電子授受などの相互作用によるものと推定される。
【０００６】
従って、シリケート中の金属量を増やすことが、生成したカーボンナノチューブの質、量を向上することにつながることが予測できる。しかし、結晶性メタロシリケートゼオライトに多くの金属を導入することは非常に困難である。しかも、ゼオライトは合成時に高価なテンプレート化合物を使うことが一般的で触媒の担体（支持体）としては、高価であるという欠点を有していた。
【０００７】
【発明が解決しようとする課題】
本発明は、上記従来技術の欠点を克服して、良質のカーボンナノチューブを安価に製造できうる触媒を提供し、それを用いたカーボンナノチューブの製造方法を提供することをその課題とする。
【０００８】
【課題を解決するための手段】
本発明者らは、前記課題を解決すべく鋭意研究を重ねた結果、非晶質メタロシリケートであれば、多くの金属を骨格中に導入できること、それを焼成して結晶としたものもゼオライトのように結晶内に均一な多孔を持たないものであれば、高価なテンプレートを使わずに安価に製造できるだけでなく、これらを支持体としたものでも高品質のカーボンナノチューブが得られることを見出し、本発明を完成するに至った。また、非晶質メタロシリケートと同様に結晶質無多孔のメタロシリケートを支持体とし、その支持体結晶表面に金属が担持されているものも課題解決に有効であることを見いだした。
【０００９】
すなわち本発明は、骨格中の金属が遷移金属である非晶質メタロシリケートを支持体とし、その支持体に金属が担持されていることを特徴とする触媒と炭素含有化合物を５００〜１２００℃で接触させることを特徴とするカーボンナノチューブの製造方法、骨格中の金属が遷移金属である非晶質メタロシリケートを焼成して得られる結晶質無多孔のメタロシリケートを支持体とし、その支持体結晶表面に金属が担持されていることを特徴とする触媒と炭素含有化合物を５００〜１２００℃で接触させることを特徴とするカーボンナノチューブの製造方法、および骨格中の金属が遷移金属である非晶質メタロシリケート又はそれを焼成して得られる結晶質無多孔のメタロシリケート上に金属が担持されていることを特徴とするカーボンナノチューブ製造用触媒組成物である。
【００１０】
【発明の実施の形態】
以下本発明について詳述する。本発明の方法は、骨格中の金属が遷移金属である非晶質メタロシリケートを支持体とし、その支持体に金属が担持されていることを特徴とする触媒と炭素含有化合物を５００〜１２００℃で接触させることを特徴とするカーボンナノチューブの製造方法である。
【００１１】
本発明において非晶質メタロシリケートとは、Si-O-Me(Meは金属）の結合を有する非晶質の酸化物である。このような化合物の製造方法は、特に限定されないが、例えば珪素を含む水溶液と金属を含む水溶液を混ぜて、酸性物質、又は塩基性物質の存在下攪拌、場合によっては加熱して、珪素の水酸化物と金属の水酸化物の縮合を進行させ析出した非晶質メタロシリケートを水洗、乾燥、必要に応じて焼成する方法が挙げられる。金属は高分散に存在する方が、好ましい。それは、最終的に担持する触媒金属が高分散に担持されることと、触媒金属との相互作用効果が顕著に現れるためである。メタロシリケートの金属を高分散に分散させる方法は、特に制限はないが、たとえば、アルコキシド化合物を使う方法が好ましく用いられる。珪素のアルコキシド化合物を含有する溶液と金属のアルコキシドを有する溶液を混合し、水と触媒となる塩基性物質、酸性物質を添加し、アルコキシドの加水分解と生成した水酸化物の縮合を進めることにより、非晶質メタロシリケートを生成させる。この方法は原子レベルで珪素と金属が溶解し分散した状態から酸化物を作っていくので、高分散となる。本発明において非晶質は、珪素、酸素、金属の並び方に結晶性が無いことを言う。非晶質のメタロシリケートが集まって規則正しく並んだメソポーラス材料は本発明では非晶質と定義する。その理由は、メソポーラスが形成している壁が非晶質だからである。本発明で非晶質であることの利点は、金属触媒に好影響を与えるメタロシリケートの金属をシリケート中に必要なだけ導入できることであり、骨格が非晶質であるから、骨格組成を自由にコントロールできる。
【００１２】
骨格に入れる金属は、遷移金属であれば特に限定されないが、 Sc,Y,La,Ti,Zr,V,Nb,Cr,Mo,W,Mn,Fe,Ru,Co,Ni,Cu,Zn等が好ましい。その理由は、明らかではないが、遷移金属のｄ軌道が担持された金属触媒との電子の授受に携わり好影響を与えるものと思われる。２種類以上の金属を使っても構わない。
【００１３】
非晶質メタロシリケートは、自由に骨格の組成をコントロールできるが、数多くの未結合のＯＨ基が存在している。これらは、金属を担持する際結合手になる等利点もあるが、高温でお互い縮合する時に担持された金属が凝集するなどの望ましくないこともある。そのために、予め反応温度で焼成してから、金属を含む化合物を担持し、触媒として用いることが好ましい。しかし、焼成により非晶質が結晶質に変わる場合があるが、それは構わない。先に述べたように、シリケート構造に多くの金属原子を導入することが目的であり、結晶であろうと、非晶質であろうとどちらでも良い。結晶内に細孔があるゼオライトのような物質は、（１）熱的に不安定である、（２）カーボンナノチューブの生成に使用されないゼオライト細孔内に貴重な金属触媒が入ってしまうという欠点がある。従って、結晶性のメタロシリケートでも無多孔のものがよい。ここで無多孔とは、液体窒素温度（７７Ｋ）で窒素ガス吸着で測定したときに窒素１０ｋＰａ（大気圧の０．１倍）での窒素吸着量が０．０５ｇ／ｇ以下であることをいう。結晶表面に金属が担持されることが重要であり、無多孔で微結晶のものが表面積が高く好ましい。結晶の大きさは、特に制限はないが、好ましくは１０μｍ以下である。更に好ましくは１μｍ以下である。結晶の大きさはＦＥ−ＳＥＭで確認できる。
【００１４】
非晶質のメタロシリケートや微結晶のメタロシリケートは、表面OH基が多く存在する。これらのOH基はカーボンナノチューブ生成温度において縮合し、表面構造が変わり、その際に表面に担持されている触媒金属が凝集してしまい、単層から５層の細いカーボンナノチューブを得る際には好ましくない。このようなことを防ぐためには、支持体は一度反応温度以上で焼成することが好ましい。特に結晶性の低い支持体、微結晶の支持体を使用する場合は、その組成に関わらず好ましい。
【００１５】
また、本発明は骨格中の金属が遷移金属である非晶質メタロシリケートを焼成して得られる結晶質無多孔のメタロシリケートを支持体とし、その支持体結晶表面に金属が担持されている触媒も使用する。さらに、非晶質メタロシリケートの支持体を反応温度以上の温度で焼成した後、触媒金属を含む化合物を担持し、非酸化性ガス中で反応温度まで昇温し、反応温度になった後炭素含有原料を導入することを特徴とするカーボンナノチューブの製造方法も本発明の好ましい方法である。本方法においては、一度、支持体を反応温度以上に焼成した後、金属を担持する事が重要である。一度反応温度以上で焼成することにより、反応温度で構造変化な どのない安定な支持体となるからである。支持体を焼成する場合の雰囲気は、特に限定されない。非酸化性ガスとは、例えば、Ｈｅ，Ａｒ，Ｎ2，Ｈ2等のことである。
【００１６】
非晶質のメタロシリケート、結晶性メタロシリケートで且つ無多孔の支持体は粉末状でも良いが、膜状でも良い。膜状にした場合、カーボンナノチューブを配向して成長させることが出来好ましい。
【００１７】
本発明において、触媒は、非晶質メタロシリケート、結晶質無多孔のメタロシリケートの表面に金属が担持されていることが必須である。金属の種類は、特に限定されないが、３〜１２族の金属、特に好ましくは、５〜１１族が好ましく用いられる。中でも、Ｖ，Ｍｏ，Ｆｅ，Ｃｏ，Ｎｉ等は特に好ましく用いられる。一種類だけ担持されていても、二種類以上担持されていてもかまわない。２種類以上担持させる方が好ましい。２種類の場合は、Ｃｏと他の金属の組み合わせが特に好ましい。ＣｏとＦｅ，Ｎｉ，Ｖ，Ｍｏの組み合わせが最も好ましい。更に第３成分を添加することも好ましく行われる。支持体への担持方法は、特に限定されないが、例えば、担持したい金属の塩を溶解させた非水溶液中（例えばエタノール溶液）又は水溶液中に、支持体を含浸し、充分に分散混合した後、乾燥させ、非酸化性ガス中で高温（３００〜６００℃）で加熱することによって、支持体に金属を担持することができる（含浸法）。又は、金属塩の水溶液に支持体を含浸し、含浸法で金属塩を担持し、乾燥させ、非酸化性ガス中で高温（３００〜６００℃）で加熱することによって、支持体に金属を担持することもできる。金属塩を担持して不活性ガス中で焼成することにより、厳密な意味で、金属として担持されているかどうかは不明であるが、本発明において触媒となる金属は金属塩を不活性ガス中で３００℃以上で焼成したものも含む。ここで非酸化性ガスとは例えばＨｅ，Ａｒ，Ｎ2，Ｈ2等のことである。勿論、金属塩を担持した後、空気中で焼成して金属酸化物とした後、水素を使用して還元して耐熱性ゼオライト結晶表面に金属を担持することもできる。担持される金属の大きさは、数nm〜数１０nmの範囲である。好ましくは、１nm〜２０nmであり、特に好ましくは、１〜１０nmである。金属塩溶液の濃度を制御することによって、金属の大きさは制御することが可能である。金属の大きさは、触媒サンプルを超薄切片法で切り出し、透過型電子顕微鏡で観察することにより測定できる。金属の担持量は、特に限定されないが、金属重量として、１〜２０％、好ましくは２〜１２％である。
【００１８】
本方法では、非晶質メタロシリケートまたは無多孔の結晶質メタロシリケートを支持体とし、その支持体表面に金属が担持されていることを特徴とする触媒と炭素含有化合物を５００〜１２００℃で接触させる。使用する炭素含有化合物は、特に限定されないが、炭化水素及び一酸化炭素が考えられる。炭化水素は芳香族、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であってよい。あるいは、前記炭化水素は非芳香族、例えばメタン、エタン、プロパン、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であってもよい。前記炭化水素はまた酸素を含むもの、例えばメタノールもしくはエタノールのごときアルコール、アセトンのごときケトン、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、又はこれらの混合物であってもよい。
【００１９】
接触のさせ方は、特に限定されないが、例えば、管状炉に設置された石英製の反応管内に、本発明の触媒を置き、加熱下で酸素ガスの非存在下で炭素含有化合物ガスを流すことにより達成できる。触媒と炭素含有化合物の接触方法は、上記のような方法でも触媒を噴霧する方法でもかまわない。炭素含有化合物以外のガスは、酸素ガス以外は好ましく使用される。酸素は爆発の可能性があるので使用しないが、窒素、アルゴン、水素、ヘリウム、等は好ましく使用される。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効果がある。水素は、特に触媒金属の活性化に効果があり特に好ましく用いられる。酸素も爆発限界以下であれば使用しても構わない。
【００２０】
本発明でカーボンナノチューブとは、中空状で外径が５０nmより細く、内径が０．３nmより太く、１０nmより細い中空状の実質的にカーボン質のチューブのことである。チューブの壁の部分はグラファイト層でできていることが好ましい。これは高分解能透過型電子顕微鏡で確認できる。触媒、単体の組成、反応条件などによって単層から多層まで種々作りわけが可能である。特に本発明方法では、比較的欠陥の少ない高品質のカーボンナノチューブが高収率で得られる。
【００２１】
本発明方法は、種々の骨格金属をシリケート中に導入し、触媒金属と担体との相互作用を変えることにより、生成するカーボンナノチューブをコントロールできる。例えば、非晶質チタノシリケート又は結晶質無多孔チタノシリケートを支持体として、８００℃以上で本発明方法で中空状ナノファイバーを製造したとき、単層〜５層の細いカーボンナノチューブが選択的にできる。
【００２２】
更に、高品質のカーボンナノチューブを作ることができることになった最も重要な因子である触媒組成物も本発明に含まれる。すなわち、非晶質又は結晶質無多孔のメタロシリケート上に金属が担持されていることを特徴とするカーボンナノチューブ製造用触媒組成物である。非晶質又は結晶質無多孔のメタロシリケートの定義は、前述の通りである。
【００２３】
本発明を以下の実施例によりさらに詳細に説明する。もっとも、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限定的に解釈してはならない。
【００２４】
【実施例】
（実施例１）
［非晶質チタノシリケートの合成］
２０ｇのテトラエチルオルソシリケート（和光純薬工業株式会社製）を１００ｇのエタノール（和光純薬工業株式会社製）に添加し攪拌した。１０ｇチタニウムテトライソプロポキシド（和光純薬工業株式会社製）を２００ｇのイソプロパノール（和光純薬工業株式会社製）に添加し攪拌した。上記２つの液を混合し攪拌した。更に、攪拌しながら、３０ｇのアンモニア水（２５〜２７．９％：和光純薬工業株式会社製）を加えて１時間攪拌した。その後、ロータリーエバポレーターで乾燥させた。乾燥品をＸ線回折測定を行ったところ、非晶質に特有のハロー図形が得られた。
［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）０．０８ｇと酢酸コバルト４水和物（ナカライテスク）社製）０．１１ｇ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。ここに１．０ｇの上記非晶質チタノシリケート粉末を加え、超音波洗浄機で１０分間処理し、６０℃恒温下でメタノールを除去して得た。
【００２５】
［カーボンナノチューブの合成（６００℃）］
内径３０ｍｍの石英管の中央部に石英プレート上に金属塩を担持した非晶質チタノシリケートを０．０５７ｇ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。得られた反応物を日本電子データム（株）走査電子顕微鏡ＪＳＭ−６３０１ＮＦで観察したところ、ほとんど非晶質のカーボン質が堆積は無かった。ファイバー状物質の形状を透過型電子顕微鏡で測定したところ、外径が３０ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーが主成分であることがわかった。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グラファイト層で構成されていた。
【００２６】
［ナノファイバーの合成（９００℃）］
内径３０ｍｍの石英管の中央部に石英プレート上に金属塩を担持した非晶質チタノシリケートを０．０３４ｇ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９００℃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。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グラファイト層で構成されていた。更に単層、２層のカーボンナノチューブも見られた。
【００２７】
（実施例２）
［非晶質チタノシリケートの焼成］
実施例１で合成したチタノシリケート粉末を空気中９００℃で１時間焼成した。焼成後の粉末をＸ線回折測定をしたところ、結晶性のピークが現れた。ゼオライト系のピークではなかった。このサンプルの液体窒素温度での窒素吸着を測定したところ、マイクロポアに起因する吸着は、０．０１ｇ／ｇ以下であった。
【００２８】
［焼成後チタノシリケー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。ここに１．０ｇの上記焼成後チタノシリケートを加え、超音波洗浄機で１０分間処理し、６０℃恒温下でメタノールを除去して得た。
【００２９】
［ナノファイバーの合成（６００℃）］
内径３０ｍｍの石英管の中央部に石英プレート上に金属塩を担持した結晶質無孔チタノシリケートを０．０５０ｇ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。石英プレート上に堆積した反応物を日本電子データム（株）走査電子顕微鏡ＪＳＭ−６３０１ＮＦで観察したところ、ほとんど非晶質のカーボン質が堆積は無かった。ファイバー状物質の形状を透過型電子顕微鏡で測定したところ、外径が３０ｎｍ以下で内径が５ｎｍ程度の細い中空状ナノファイバーが主成分であることがわかった。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グラファイト層で構成されていた。
【００３０】
［ナノファイバーの合成（９００℃）］
内径３０ｍｍの石英管の中央部に石英プレート上に金属塩を担持した上記結晶性チタノシリケートを０．０３４ｇ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９００℃に加熱した。９００℃到達後、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。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グラファイト層で構成されていた。更に単層、２層のカーボンナノチューブも見られた。実施例１の時より、多く単層、２層のカーボンナノチューブが得られていた。
【００３１】
【発明の効果】
本発明方法によると、ほとんど非晶質のカーボン質の堆積無く、非常に質の良い細い黒鉛質のカーボンナノチューブが収率良く得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a carbon nanotube having a high surface area, a high elastic Young's modulus, a high tensile strength, and a high conductivity. According to the present invention, thin carbon nanotubes of less than 10 nm can be obtained.
[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 referred to as a single-walled carbon nanotube, and a multi-walled carbon nanotube is referred to as a multilayered one.
[0003]
Known methods for producing carbon nanotubes include arc discharge methods and chemical vapor deposition (CVD) methods. The arc discharge method uses a carbon rod as an electrode in a vacuum or in an inert gas atmosphere to produce a high-voltage, high-current arc discharge to produce carbon nanotubes. Carbon nanotubes are graphite, Obtained together with carbon nanoparticles. In the CVD method, carbon nanotubes are produced by reacting a raw material gas at several hundred degrees in the presence of fine metal particles such as iron and nickel. In this case, benzene, toluene, orthomethyl diallyl ketone, acetylene, ethylene, methane, or the like is used as the source gas. Carbon nanotubes produced by the arc discharge method can produce nanotubes with few defects in the graphite layer, but are rich in impurities such as amorphous carbon. In the CVD method, carbon nanotubes can be produced at a low cost with few impurities, but the produced carbon nanotubes have many defects in the graphite layer, and most of them do not form a graphite layer with few defects unless heat treatment at about 2900 ° C. It is.
[0004]
As a means for solving this, Shinohara et al. Reported that multi-walled carbon nanotubes with few defects can be produced using a catalyst in which cobalt and vanadium are supported on Y-type zeolite (Chemical Physics Letters 303 (1999) 117). -124).
[0005]
The present inventors have found that a multi-walled carbon nanotube and a single-walled carbon nanotube with better crystallinity can be obtained by further supporting a metal catalyst on a crystalline metallosilicate zeolite. This cause is presumed to be due to interactions such as electron transfer between the metal present in the silicate skeleton and the supported metal catalyst.
[0006]
Therefore, it can be predicted that increasing the amount of metal in the silicate will lead to improvement in the quality and amount of the produced carbon nanotubes. However, it is very difficult to introduce many metals into the crystalline metallosilicate zeolite. In addition, zeolite generally uses an expensive template compound at the time of synthesis, and has a disadvantage that it is expensive as a catalyst support (support).
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a catalyst capable of overcoming the above-mentioned drawbacks of the prior art and capable of producing high-quality carbon nanotubes at low cost, and to provide a method for producing carbon nanotubes using the catalyst.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the inventors of the present invention can introduce a large amount of metal into the skeleton if it is an amorphous metallosilicate. As such, if it does not have a uniform porosity in the crystal, it can be produced at low cost without using an expensive template, and it can be found that high quality carbon nanotubes can be obtained even using these as a support, The present invention has been completed. In addition, it has been found that a non-porous metallosilicate similar to an amorphous metallosilicate as a support and a metal supported on the surface of the support crystal is effective in solving the problem.
[0009]
That is, the present invention provides a catalyst and a carbon-containing compound characterized in that an amorphous metallosilicate whose metal in the skeleton is a transition metal is used as a support and the metal is supported on the support at 500 to 1200 ° C. A method for producing carbon nanotubes characterized by contact, a crystalline nonporous metallosilicate obtained by firing amorphous metallosilicate whose metal in the skeleton is a transition metal as a support, and the support crystal surface amorphous metallo method of manufacturing carbon nanotubes comprising contacting the catalyst with the carbon-containing compound in which the metal is characterized in that it is carried at 500 to 1200 ° C., and metal skeleton is a transition metal carbon nano-Ju metal on metallosilicate crystalline non porous obtained by silicate or calcined products is characterized in that it is carried A Bed catalyst composition for producing.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below. According to the method of the present invention, an amorphous metallosilicate in which the metal in the skeleton is a transition metal is used as a support, and the catalyst and the carbon-containing compound are supported on the support at 500 to 1200 ° C. It is the manufacturing method of the carbon nanotube characterized by making it contact.
[0011]
In the present invention, the amorphous metallosilicate is an amorphous oxide having a bond of Si—O—Me (Me is a metal). The method for producing such a compound is not particularly limited. For example, an aqueous solution containing silicon and an aqueous solution containing a metal are mixed, stirred in the presence of an acidic substance or a basic substance, and heated in some cases to obtain an aqueous solution of silicon. Examples thereof include a method in which condensation of an oxide and a metal hydroxide proceeds to wash the deposited amorphous metallosilicate, dry it, and fire it as necessary. The metal is preferably present in high dispersion. This is because the catalyst metal to be finally supported is supported in a highly dispersed state and the interaction effect with the catalyst metal appears remarkably. The method for dispersing the metallosilicate metal in a highly dispersed manner is not particularly limited, but for example, a method using an alkoxide compound is preferably used. By mixing a solution containing a silicon alkoxide compound and a solution containing a metal alkoxide, adding water and a basic substance or acidic substance as a catalyst, and proceeding with hydrolysis of the alkoxide and condensation of the generated hydroxide To produce amorphous metallosilicate. In this method, an oxide is formed from a state in which silicon and metal are dissolved and dispersed at an atomic level, so that the dispersion becomes high. In the present invention, amorphous means that there is no crystallinity in the arrangement of silicon, oxygen, and metal. In the present invention, an amorphous mesoporous material in which amorphous metallosilicates are gathered and regularly arranged is defined as amorphous. The reason is that the wall formed by the mesoporous is amorphous. The advantage of being amorphous in the present invention is that a metallosilicate metal that has a positive influence on the metal catalyst can be introduced into the silicate as much as necessary. Since the skeleton is amorphous, the skeleton composition can be freely set. I can control it.
[0012]
Metal Add to skeleton is not particularly limited as long as it is a transition metal, Sc, Y, La, Ti , Zr, V, Nb, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Cu, Zn , etc. Is preferred. The reason for this is not clear, but it is considered that it is positively affected by the transfer of electrons to and from the metal catalyst carrying the transition metal d-orbitals. Two or more kinds of metals may be used.
[0013]
Amorphous metallosilicate can freely control the composition of the skeleton, but there are many unbound OH groups. These have the advantage of becoming a bond when the metal is supported, but may be undesirable, for example, the supported metals may aggregate when condensed with each other at a high temperature. For this purpose, it is preferable to calcine at a reaction temperature in advance and then to support a compound containing a metal and use it as a catalyst. However, there is a case where the amorphous state is changed to crystalline state by firing, but that is not a problem. As described above, the purpose is to introduce a large number of metal atoms into the silicate structure, which may be crystalline or amorphous. Substances such as zeolite with pores in the crystal have the following disadvantages: (1) Thermally unstable, (2) Precious metal catalyst enters zeolite pores that are not used to produce carbon nanotubes There is. Accordingly, it is preferable that the crystalline metallosilicate is nonporous. Here, non-porous means that the nitrogen adsorption amount at 10 kPa of nitrogen (0.1 times the atmospheric pressure) is 0.05 g / g or less when measured by nitrogen gas adsorption at a liquid nitrogen temperature (77 K). . It is important that a metal is supported on the crystal surface, and a non-porous and microcrystalline material has a high surface area and is preferable. The size of the crystal is not particularly limited, but is preferably 10 μm or less. More preferably, it is 1 μm or less. The size of the crystal can be confirmed by FE-SEM.
[0014]
Amorphous metallosilicate and microcrystalline metallosilicate have many surface OH groups. These OH groups condense at the carbon nanotube production temperature, the surface structure changes, and the catalyst metal supported on the surface agglomerates, which is preferable when obtaining thin carbon nanotubes of single to five layers. Absent. In order to prevent this, the support is preferably baked once at the reaction temperature or higher. In particular, when a low crystalline support or a microcrystalline support is used, it is preferable regardless of its composition.
[0015]
The present invention also provides a catalyst in which a crystalline non-porous metallosilicate obtained by firing amorphous metallosilicate whose metal in the skeleton is a transition metal is used as a support, and the metal is supported on the support crystal surface. Also used. Further, after firing the support amorphous Metaroshirike preparative reaction temperature or higher, a compound containing a catalytic metal supported, heated in a non-oxidizing gas to the reaction temperature, the carbon after becoming reaction temperature A method for producing a carbon nanotube, which is characterized by introducing a containing raw material, is also a preferred method of the present invention. In this method, it is important to support the metal after the support is once fired to the reaction temperature or higher. This is because once firing at a temperature higher than the reaction temperature, a stable support with no structural change at the reaction temperature is obtained. The atmosphere in the case of baking a support body is not specifically limited. The non-oxidizing gas is, for example, He, Ar, N 2 , H 2 or the like.
[0016]
The amorphous metallosilicate, crystalline metallosilicate and non-porous support may be in the form of a powder or a film. When it is made into a film, carbon nanotubes can be oriented and grown, which is preferable.
[0017]
In the present invention, it is essential that the catalyst has a metal supported on the surface of amorphous metallosilicate or crystalline non-porous metallosilicate. Although the kind of metal is not specifically limited, The group 3-12 metal, Especially preferably, the group 5-11 is used preferably. Among these, V, Mo, Fe, Co, Ni and the like are particularly preferably used. Only one type may be supported, or two or more types may be supported. Two or more types are preferably supported. In the case of two types, a combination of Co and another metal is particularly preferable. A combination of Co and Fe, Ni, V, Mo is most preferred. It is also preferable to add a third component. The supporting method on the support is not particularly limited. For example, the support is impregnated in a non-aqueous solution (for example, ethanol solution) or an aqueous solution in which a metal salt to be supported is dissolved, and sufficiently dispersed and mixed. The metal can be supported on the support by drying and heating in a non-oxidizing gas at a high temperature (300 to 600 ° C.) (impregnation method). Alternatively, the support is impregnated in an aqueous solution of a metal salt, the metal salt is supported by the impregnation method, dried, and heated at a high temperature (300 to 600 ° C.) in a non-oxidizing gas, thereby supporting the metal on the support. You can also It is unclear whether it is supported as a metal in a strict sense by supporting a metal salt and calcining it in an inert gas, but the metal used as a catalyst in the present invention is a metal salt in an inert gas. Including those fired at 300 ° C or higher. Here, the non-oxidizing gas is, for example, He, Ar, N 2 , H 2 or the like. Of course, after the metal salt is supported, it can be fired in air to form a metal oxide, and then reduced using hydrogen to support the metal on the surface of the heat-resistant zeolite crystal. The size of the metal to be supported is in the range of several nm to several tens of nm. Preferably, it is 1 nm to 20 nm, and particularly preferably 1 to 10 nm. By controlling the concentration of the metal salt solution, the size of the metal can be controlled. The size of the metal can be measured by cutting a catalyst sample by an ultrathin section method and observing it with a transmission electron microscope. The amount of metal supported is not particularly limited, but is 1 to 20%, preferably 2 to 12% as the metal weight.
[0018]
In this method, an amorphous metallosilicate or a non-porous crystalline metallosilicate is used as a support, and the catalyst is characterized in that a metal is supported on the surface of the support and a carbon-containing compound is contacted at 500 to 1200 ° C. Let The carbon-containing compound used is not particularly limited, but hydrocarbons and carbon monoxide are considered. The hydrocarbon may be aromatic, such as benzene, toluene, xylene, cumene, ethylbenzene, diethylbenzene, trimethylbenzene, naphthalene, phenanthrene, anthracene or mixtures thereof. Alternatively, the hydrocarbon may be non-aromatic, such as methane, ethane, propane, ethylene, propylene or acetylene or mixtures thereof. The hydrocarbon may also contain oxygen, such as alcohols such as methanol or ethanol, ketones such as acetone, and aldehydes such as formaldehyde or acetaldehyde, or mixtures thereof.
[0019]
The contacting method is not particularly limited. For example, the catalyst of the present invention is placed in a quartz reaction tube installed in a tubular furnace, and the carbon-containing compound gas is allowed to flow in the absence of oxygen gas under heating. Can be achieved. The contact method of the catalyst and the carbon-containing compound may be the above method or a method of spraying the catalyst. Gases other than carbon-containing compounds are preferably used other than oxygen gas. Oxygen is not used because it may explode, but nitrogen, argon, hydrogen, helium, etc. are preferably used. These gases are effective for controlling the concentration of the carbon-containing compound gas and as a carrier gas. Hydrogen is particularly preferred because it has an effect on activation of the catalyst metal. Oxygen may be used as long as it is below the explosion limit.
[0020]
In the present invention, the carbon nanotube is a hollow, substantially carbonaceous tube having a hollow shape with an outer diameter smaller than 50 nm, an inner diameter larger than 0.3 nm, and smaller than 10 nm. The wall portion of the tube is preferably made of a graphite layer. This can be confirmed with a high-resolution transmission electron microscope. Depending on the catalyst, the composition of the simple substance, the reaction conditions, etc., various forms can be made from a single layer to multiple layers. In particular, in the method of the present invention, high-quality carbon nanotubes with relatively few defects can be obtained in a high yield.
[0021]
In the method of the present invention, carbon nanotubes to be produced can be controlled by introducing various skeletal metals into the silicate and changing the interaction between the catalyst metal and the support. For example, when hollow nanofibers are produced by the method of the present invention at a temperature of 800 ° C. or higher using amorphous titanosilicate or crystalline nonporous titanosilicate as a support, single- to thin-walled carbon nanotubes are selectively used. Can be.
[0022]
Furthermore, the catalyst composition which is the most important factor that has made it possible to produce high-quality carbon nanotubes is also included in the present invention. That is, the catalyst composition for producing carbon nanotubes is characterized in that a metal is supported on an amorphous or crystalline nonporous metallosilicate. The definition of the amorphous or crystalline nonporous metallosilicate is as described above.
[0023]
The invention is illustrated in more detail by the following examples. However, the following examples are given for illustrative purposes and should not be construed as limiting in any way.
[0024]
【Example】
Example 1
[Synthesis of amorphous titanosilicate]
20 g of tetraethyl orthosilicate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 100 g of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) and stirred. 10 g titanium tetraisopropoxide (Wako Pure Chemical Industries, Ltd.) was added to 200 g of isopropanol (Wako Pure Chemical Industries, Ltd.) and stirred. The above two liquids were mixed and stirred. Furthermore, 30 g of ammonia water (25 to 27.9%: manufactured by Wako Pure Chemical Industries, Ltd.) was added with stirring, and the mixture was stirred for 1 hour. Then, it was dried with a rotary evaporator. When the dried product was subjected to X-ray diffraction measurement, a halo figure peculiar to amorphous was obtained.
[Support of metal salt on heat-resistant zeolite]
Ferrous acetate (Aldrich) 0.08 g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.11 g are added to 7 ml of methanol (Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this, 1.0 g of the above amorphous titanosilicate powder was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C.
[0025]
[Synthesis of carbon nanotubes (600 ° C)]
0.057 g of amorphous titanosilicate carrying a metal salt on a quartz plate was taken at the center of a quartz tube having an inner diameter of 30 mm, 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. When the obtained reaction product was observed with a scanning electron microscope JSM-6301NF of JEOL Datum Co., Ltd., almost no amorphous carbon was deposited. When the shape of the fiber-like substance was measured with a transmission electron microscope, it was found that thin hollow nanofibers having an outer diameter of 30 nm or less and an inner diameter of about 5 nm were the main components. When the hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of graphite layers.
[0026]
[Synthesis of nanofiber (900 ℃)]
0.034 g of amorphous titanosilicate carrying a metal salt on a quartz plate was taken at the center of a quartz tube having an inner diameter of 30 mm, and nitrogen was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 900 ° 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. When the shape of a part of the reaction product deposited on the quartz plate was measured with a transmission electron microscope, it was a hollow nanofiber. When the hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of graphite layers. In addition, single-walled and double-walled carbon nanotubes were also observed.
[0027]
(Example 2)
[Baking of amorphous titanosilicate]
The titanosilicate powder synthesized in Example 1 was calcined in air at 900 ° C. for 1 hour. When the powder after firing was subjected to X-ray diffraction measurement, a crystalline peak appeared. It was not a zeolitic peak. When the nitrogen adsorption of this sample at the liquid nitrogen temperature was measured, the adsorption due to the micropores was 0.01 g / g or less.
[0028]
[ Support of metal salt on titanosilicate after firing ]
Ferrous acetate (Aldrich) 0.08 g and cobalt acetate tetrahydrate (Nacalai Tesque) 0.11 g were added to 7 ml of methanol (Nacalai Tesque) and suspended in an ultrasonic cleaner for 10 minutes. did. To this, 1.0 g of the titanosilicate after calcination was added, treated with an ultrasonic cleaner for 10 minutes, and methanol was removed at a constant temperature of 60 ° C.
[0029]
[Synthesis of nanofiber (600 ℃)]
0.050 g of crystalline non-porous titanosilicate carrying a metal salt on a quartz plate was taken at the center of a quartz tube having an inner diameter of 30 mm, 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. When the reaction product deposited on the quartz plate was observed with a scanning electron microscope JSM-6301NF, JEOL Datum Co., Ltd., almost no amorphous carbon was deposited. When the shape of the fibrous material was measured with a transmission electron microscope, it was found that thin hollow nanofibers having an outer diameter of 30 nm or less and an inner diameter of about 5 nm were the main components. When the hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of graphite layers.
[0030]
[Synthesis of nanofiber (900 ℃)]
0.034 g of the above crystalline titanosilicate having a metal salt supported on a quartz plate was taken at the center of a quartz tube having an inner diameter of 30 mm, and nitrogen was supplied at 30 ml / min. The quartz tube was placed in an electric furnace and the center temperature was heated to 900 ° C. After reaching 900 ° C., ultra high purity acetylene gas (manufactured by High Pressure Gas Industry) was supplied at 1 ml / min for 30 minutes, and then the supply of acetylene gas was stopped and the temperature was cooled to room temperature. When the shape of a part of the reaction product deposited on the quartz plate was measured with a transmission electron microscope, it was a hollow nanofiber. When the hollow nanofibers were observed with a high-resolution transmission electron microscope, the walls of the nanofibers were composed of graphite layers. In addition, single-walled and double-walled carbon nanotubes were also observed. More single-walled and double-walled carbon nanotubes were obtained than in Example 1.
[0031]
【The invention's effect】
According to the method of the present invention, fine graphite carbon nanotubes of very high quality can be obtained with high yield without almost amorphous carbonaceous deposits.
Claims (4)
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| JP3913181B2 (en) | 2003-02-06 | 2007-05-09 | 三菱重工業株式会社 | Carbon nanofiber manufacturing method and manufacturing apparatus |
| CN100553016C (en) * | 2004-08-26 | 2009-10-21 | 松下电器产业株式会社 | Composite particles for electrode use and manufacture method thereof and secondary cell |
| US7485600B2 (en) * | 2004-11-17 | 2009-02-03 | Honda Motor Co., Ltd. | Catalyst for synthesis of carbon single-walled nanotubes |
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| EP1845064A4 (en) * | 2005-02-02 | 2008-10-15 | Otsuka Chemical Co Ltd | Carbon nanotube-loaded inorganic particle |
| US20110038785A1 (en) * | 2008-03-17 | 2011-02-17 | Otsuka Chemical Co., Ltd. | Method for manufacturing carbon nanotube |
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