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

本研究旨在开发新型催化剂来制备形状可控的碳纳米管(CNT)，在我们独创的纳米技术的基础上制备成分和结构可控的金属纳米粒子。在这里，我们制备了由Pd核和过渡金属(Ni，Co，Fe)壳组成的二元金属纳米粒子作为活性催化物种。以负载型二元金属催化剂为载体，在不同条件下制备了碳纳米管，并对其形貌、结构和晶型进行了表征。主要研究结果如下：1.不同的催化剂载体对碳纳米管的产率和形貌有较大影响。例如，碳纳米管的产率高于硅铝载体。有趣的是，在氧化镁载体上制备出了直径恒定的超长碳纳米管。这样的碳纳米管有望成为器件应用。2.不同原料气体对碳纳米管结构的影响较大。当使用乙炔时，无论反应温度如何，都可以得到直径恒定的碳纳米管，直径约为20次。另一方面，由乙烯制备的碳纳米管直径较大，且随反应温度的升高而增大。3.以乙炔为原料制备的碳纳米管具有与碳纳米管轴线平行排列的六方碳片，而以乙烯为原料制备的碳纳米管基本上为非晶态。以乙烯为原料制得的碳纳米管具有与碳纳米管轴线成一定角度的短片状结构，这可能反映了二元金属催化剂特殊的核壳结构。4.二元金属催化剂中过渡金属(Ni、Co、Fe)对碳纳米管的影响中等。

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.