Conducting catalytic methane decomposition over Fe catalysts is a green and economic route to produce H-2 without CO/CO2 contamination. Fused 65 wt% and impregnated 20 wt% Fe catalysts were synthesized with different additives to investigate their activity, whereas showing Fe-Al2O3 combination as the best catalyst. Al2O3 is speculated to expose more Fe for the selective deposition of carbon nano tubes (CNTS). A fused Fe (65 wt%)-Al2O3 sample was further investigated by means of H-2-TPR, in-situ XRD, HRTEM and XAS to conclude 750 degrees C is the optimized temperature for H-2 pre-reduction and reaction to obtain a high activity. Based on density functional theory (DFT) study, a reaction mechanism over Fe catalysts was proposed to explain the formation of graphite from unstable supersaturated iron carbides decomposition. A carbon deposition model was further proposed which explains the formation of different carbon nano materials. (C) 2017 Elsevier B.V. All rights reserved.