Abstract
Multi‐walled carbon nanotubes (MWCNTs) are prepared by chemical vapor deposition (CVD) in C~2~H~6~ + H~2~ mixture over 20%Fe/SiO~2~ catalysts. The effects, in terms of yield and selectivity of the growth process, of the changes in composition (H~2~ at 0–75%) and flow‐rate (100–150 sccm) of gas‐mixture, catalyst reduction‐temperature (400 °C and 650 °C), temperature (750–850 °C) and duration (0.5−6 h) of the synthesis‐reaction are investigated. Although yield to C deposits improves by increasing gas flow‐rate, temperature or duration of the synthesis‐reaction, and by diminishing H~2~ volume fraction in growth atmosphere, it never exceeds 90% due to the heavy catalyst encapsulation. Moreover, the results of morphological and structural analyses show that a loss of selectivity towards nanotubes and a deterioration of CNT crystalline quality generally accompany the yield enhancement. This suggests the unsuitability of the ethane decomposition over silica‐supported Fe‐catalysts to the large‐scale production of CNTs. Nevertheless, the nanotubes attained might be profitably used in all applications exploiting the magnetic properties originating from the encapsulated iron. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)