The efficiency of iron-catalysts in hydrocarbon
decomposition, aimed at growth of carbon nanotubes by chemical vapour
deposition (CVD), is systematically investigated. The synthesis reaction is
carried out at different temperatures (873–1123 K), for
various durations (0.5–6.0 h), using diverse precursor
gases (C2H6 or C4H10) and catalyst supports (SiO2
or Al2O3). A large variety of experimental conditions is explored
by varying amount (0.5–2.0 g), metal load (20 wt.%
and 29 wt.%) and annealing temperature (723–973 K)
of the catalysts and by considering different gas flowing setups, namely, by
changing flow rate (100–240 cc/min) and composition
(H2/precursor/He, with He at 0–63%) of the gas mixture,
flow-rates and flow-ratio of reactant gases (H2:
0–120 cc/min; Precursor Gas:
15–120 cc/min; H2/PG: 0–3). Iron
catalysts encapsulation is shown to be the main factor limiting C yields in
the cases considered, and its changes to be responsible for the broad yield
variations (20–910 wt.%) observed. The results of
analyses, carried out by Raman spectroscopy (RS) and complementary
diagnostics techniques, demonstrate the need of accurately tuning the
manifold growth parameters, in order to fully benefit of the advantages
potentially deriving from a proper choice of precursor gas and
catalyst-support material.