Synthesis of Carbon Nanotubes over Composition and Shape Controlled Pd Binary Metal Nanopartkle Catalysts

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This research aims to develop novel catalysts to prepare shape-controlled carbon nanotubes (CNT) based on our original nanotechnology to prepare composition- and structure-controlled metal nanoparticles. Here, we have prepared binary metal nanoparticles consisting of Pd-core and transition metal (Ni, Co, Fe)-shell as active catalytic species. CNTs prepared under various conditions over supported binary metal catalysts have been characterized, such as shape, structure, and crystalline. Principal results are summarized as follows: 1. Yields and shapes of CNTs changed significantly depending on kinds of catalyst supports. For example, CNTs produced with high yields over silica-alumina support. Interestingly, very long CNTs with constant diameter were produced over MgO support. Such CNTs may be expected as device application. 2. Structure of CNTs affected seriously by kinds of feed gases. When acetylene was used, CNTs with constant diameter of ca. 20 run were produced irrespective of the reaction temperature. On the other hand, CNTs produced from ethylene had large diameters, which increased depending on the reaction temperature. 3. CNTs produced from acetylene had developed hexagonal carbon lamellae, which arranged parallel to axis of CNTs, while those produced from ethylene were essentially amorphous. Specific CNTs with short lamellae arranged with an angle to CNT axis were produced from ethylene, which may reflect special core-shell structure of binary metal catalysts. 4. Kinds of transition metals (Ni, Co, Fe) of binary metal catalyst affect moderately to CNT.