Effect of Fe load on the synthesis of C nanotubes by isobutane decomposition over Na-exchanged montmorillonite-clay catalysts

This work is a continuation and a completion of a previous study on the synthesis of multi-walled carbon nanotubes by iron-catalyzed chemical vapor deposition over sodium-exchanged K10-montmorillonite (Na+-K10) based catalysts. The influence of iron-addition (5-25 wt.%) on the catalyst performances is investigated. By comparing results here obtained by isobutane decomposition at 700 °C with those previously achieved at 600°C by using Fe/Al2O3 catalysts upon the same gas-flowing setup (120 cm 3/min 1:1 i-C4H10 + H2), it comes out that although in both the cases the best catalytic performance is obtained for a relative (to iron) carbon-supply of ≈ 160 wt.%/min, higher specific yield is achieved over alumina supported catalysts. The possible reasons for this difference are discussed in the light of the most recent assessments on nanotube growth.