Catalyst Support and Pretreatment Effects on Carbon Nanotubes Synthesis by Chemical Vapor Deposition of Methane on Iron over SiO2, Al2O3 or MgO

In this study we report the effects of support and pretreatment conditions on growth of carbon nanotubes (CNTs) by chemical vapor deposition of methane on iron catalyst supported on MgO, silica or alumina. The iron was impregnated onto the supports, and then the samples were dried, calcined at 550°C and pretreated in either helium or hydrogen up to 1000°C before exposure to methane as a carbon source for CNTs growth. Temperature programmed reduction (TPR) of the fresh catalysts and the ones pre-treated in He and in H2 shows various interactions of the iron with supports at pretreatment conditions. The CNTs are characterized by SEM, Raman, FTIR, and TEM. The IG/ID of Raman spectroscopy are 6.2, 3.8 and 0.7 for the CNTs grown on the MgO, alumina, and silica-supported iron catalysts pretreated in helium, respectively. When the Fe/MgO catalyst is pretreated in hydrogen the IG/ID ratio dramatically reduces to 0.8. A less significant effect of pretreating of the catalysts in hydrogen is observed for silica- and alumina-supported catalysts. RBM peaks of Raman spectra along with TEM results indicate the formation of bundles of 0.8-1.2 nm single-wall as well as multiwall carbon nanotubes on the Fe/MgO catalyst pre-treated in He.