高温煅烧Mo改性的Fe／MgO催化剂用于制备管径分布均一的单壁碳纳米管

研究了在以甲烷化学气相沉积法制备单壁碳纳米管的过程中高温煅烧预处理(900℃煅烧10h)对Mo改性Fe/MgO催化剂的作用.发现这种预处理有利于Fe在催化剂中的稳定和分散,从而制备出管径均一的单壁碳纳米管.采用能谱元素分析、高分辨透射电镜、X射线衍射、比表面积测量、拉曼光谱和热重分析对样品进行了表征.结果表明,在碳纳米管生长的过程中,铁元素在催化剂表面富集,单壁碳纳米管生长于富集铁的纳米颗粒上,并存在碳管直径与铁颗粒尺寸的依赖关系.Mo存在时可煅烧形成FeMoO4复合氧化物,后者比MgFe2O4相更加稳定.Mo/Fe比例对提高单壁碳纳米管的生长密度、纯度与管径均一性等均有明显影响.上述研究对进一步精确控制制备单壁碳纳米管有重要意义.

Synthesis of Single-Walled Carbon Nanotubes with Narrow Diameter Distribution by Calcination of a Mo-Modified Fe/MgO Catalyst

The Fe-Mo/MgO catalyst for the synthesis of single-walled carbon nanotubes (SWNTs) from methane decomposition by chemical vapor deposition was pretreated by calcination at 900 °C for 10 h. A comparison of SWNT growth on the catalysts with and without Mo confirmed that Mo addition in the calcined catalyst was crucial in stabilizing and dispersing Fe nanoparticles to a small size, and thus, to synthesize SWNTs with uniform diameters. The products were characterized by energy dispersive spectroscopy, high-resolution transmission electron microscopy, X-ray diffraction, Ar adsorption, Raman spectroscopy, and thermogravimetric analysis. The results showed that Fe-rich nanoparticles were the active sites for SWNT growth and the diameter of the SWNTs depended on the size of the Fe nanoparticles. The calcination led to the formation of the FeMoO₄ phase when Mo was added, which is a more stable phase than the MgFe₂O₄ phase. The Mo/Fe ratio was also important in preparing SWNTs of high density, high purity, and with a narrow diameter distribution. These results are useful for the precise control of the synthesis of SWNTs.