催化剂中Cu含量对CVD法制备碳纳米管的影响

The Effect of Copper in the Ni/MgO Catalysts for the Production of Carbon Nanotubes via the Decomposition of Ethylene

本文以溶胶-凝胶法制备了以铜为助剂的Ni/MgO催化剂,X-射线衍射(XRD)表明,经400℃氢气处理,催化剂中只有部分镍被还原,原因是NiO和MgO间存在强相互作用,形成固溶体.XRD和程序升温还原(TPR)表明,加入铜促进了镍的还原.CO 化学吸附得出,随着催化剂中铜含量的增加,还原后催化剂表面镍原子数目增多,因此,催化剂的活性和反应寿命增加,C2H4裂解生成碳纳米管(CNT)的产率随之增加;但是,铜含量过高会引起催化剂表面镍颗粒增大,导致产物中纳米碳纤维(CNF)量增多,CNT量减少.对于约50%Ni/MgO催化剂,铜的最佳含量为4%～6%,此时得到的CNT产率最高,达36 g·g-1,质量较好(纯度高、管径均匀、石墨化程度高).

Ni/MgO catalysts promoted by copper were prepared by the sol-gel method. X-ray diffraction (XRD) showed that only part of nickel could be reduced due to the strong interaction between NiO and MgO. Both XRD and TPR (Temperature-Programmed-Reduction) indicated that the addition of copper in the catalysts promoted the reduction of nickel. The adsorption of CO revealed that the number of surface Ni atoms increased with the increase of copper content, and thereby increased the activity and lifetime of the catalysts, leading to the substantial increase of the yield of the CNT from the decomposition of ethylene. However, extra copper might increase the size of the nickel particles on the surface, enhancing the production of carbon nanofibers (CNF) instead of CNT. It seems that the addition of 4%-6% Cu in the 60% Ni/MgO catalyst lead to the formation of CNT with high yield (36 g CNT per gram of catalyst) and high quality.