Large-scale synthesis of carbon nanofibers on Ni-Fe-Al hydrotalcite derived catalysts II. Effect of Ni/Fe composition on CNF synthesis from ethylene and carbon monoxide

Carbon nanofibers (CNFs) were synthesized on a series of hydrotalcite (HT) derived Ni-Fe/Al2O3 catalysts in order to achieve optimization of quality and productivity. It was found that only the Fe catalyst is active in CO disproportionation and only the Ni catalyst is active in ethylene decomposition, whereas all catalysts are active in ethylene decomposition when the reactants are a mixture of C2H4/CO. The catalysts were characterized after CNF growth by XPS and EXAFS in order to understand the catalyst structural changes during CNF synthesis. The structure and properties of the as-synthesized CNFs were characterized by SEM, TEM, TPO and XRD to correlate the CNF structure and crystallinity with the catalyst composition and the nature of the gas precursors. Based on the experimental results a reaction mechanism was proposed. Moreover, it was demonstrated that Ni-Fe/Al2O3 catalysts derived from HT precursors are promising for controlled large-scale synthesis of CNFs.