II International Symposium on Carbon for Catalysis ABSTRACTS

PP-I-28
thermogravimetric apparatus. The yield of carbon nanotubes obtained ranges in the 20-30%
wt (with respect to total catalyst), and between 300-500% wt with respect to the active
catalytic component.
Quite interesting TEM images reveal that open-ended carbon nanotubes were obtained,
while usually CVD methods bring to close-ended carbon nanotubes. The formation of open
carbon nanotubes indicates an "End-Growth" mechanism.
Figures 1a and 1b show high resolution TEM images of one of the smallest and largest
carbon nanotubes, respectively, with details of the ordering of the carbon walls. While for the
smallest carbon nanotubes (8 nm) the graphitic sheets (10 walls) are well ordered parallel to
the growing direction of the nanotubes, an apex angle of 45 degree was found for the largest
nanotubes, suggesting a different mechanism of growing of the nanotubes (zig-zag and
armchair type, respectively) inside and outside the SBA-15 channels. In general, the smallest
nanotubes show also a lower presence of defects in the ordering of the graphitic sheets with
respect to the largest nanotubes.
a
35 walls
b
8 nm
10 walls
38 nm
Figure 1. (a) High resolution image of a small carbon nanotube with a detail of the ordering of the
carbon walls. (b) High resolution image of one of the largest carbon nanotubes.
In conclusion, this work indicates that the confinement effect due to the localization of
catalyst nanoparticles inside the well ordered channels structure of the SBA-15 support may
be not only a method to control the dimension of MWCNT, but also a method to control their
helicity, the presence of defects and the growing mechanism.
References
1 G. Gulino, R. Vieira, J. Amadou, J. Dintzer, S.. Galvagno, G. Centi, M.J. Ledoux,
C. Pham-Huu, Catalysis Today (2005), 102-103 23-28.
2 G. Gulino, R. Vieira, J. Amadou, P. Nguyen, M.J. Ledoux, S, Galvagno, G. Centi,
C. Pham-Huu, Applied Catalysis, A: General (2005), 279(1-2), 89-97.
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