Silica-supported iron catalysts were prepared using an advanced non-aqueous evaporative deposition technique, which leads to a catalyst with high extents of reduction, high CO conversions, and high C2+ hydrocarbons productivities. The catalysts were tested following an L18 orthogonal array statistical design approach. Primary independent variables affecting catalysts activity were promoter type, pretreatment gas composition, pretreatment and reaction temperature. Steady state catalytic activity is positively correlated with increasing bulk chi-carbide content for silica-supported Fe and FePt catalysts but not for FePtK. The bulk and surface carbonaceous species was both measured with high pressure in situ Mössbauer spectroscopy and TPSR-MS. A correlation between the amount of reactive?-carbon (C?) and initial catalytic activity was established. An modified method was proposed for quantitative measurement of irreversible CO site density on the iron catalysts. Finally, a comprehensive model was proposed for iron phase transformations during pretreatment, FTS and post-reaction passivation/oxidation.