Synthesis of carbon nanotubes over nickel-iron catalysts supported on alumina under controlled conditions

Carbon nanotubes (CNTs) were synthesized by catalytic decomposition of acet ylene over Fe, Ni and Fe-Ni catalysts supported on alumina. The growth of C NTs was carried out at various reaction conditions. The growth density and diameter of CNTs could be controlled by varying the catalyst composition an d the growth parameters. The growth density of CNTs increased with increasi ng the activation time of catalysts in H-2 atmosphere and/or decreasing ace tylene concentration. At 600 degreesC, higher density of CNTs was observed at 60 min for higher Fe containing catalyst, whereas at 90 min for higher N i containing catalyst. The growth density of CNTs highly increased with inc reasing reaction time from 30 to 60 min. For all the catalysts, the diamete r of CNTs decreased with increasing growth time further mainly due to hydro gen etching. Bimetallic catalysts produced narrower diameter CNTs than sing le metal catalysts. The growth of CNTs followed the tip growth mode and the CNTs were multi-walled CNTs.