tFischer–Tropsch synthesis of low molecular weight (C2C4) olefins is a valuable alternative process for theproduction of key chemicals from non-petroleum precursors such as a renewable C source like biomass.The influence of the H2treatment temperature of zirconia-supported iron catalysts on the conversionof synthesis gas has been investigated. The CO conversion rate, based on steady-state, increased withthe pretreatment temperature up to a maximum and then decreased at higher temperatures. Moreover,methane selectivity was found to decrease slightly from the lowest H2treatment temperatures (46%)to the highest ones (34%), while C2C4and C5+hydrocarbons followed an opposite trend. Presumably,methane formation takes place at highly active low coordination sites residing at corners and edges,which are more abundant on small iron carbide particles. Lower hydrocarbons are mainly produced atterrace sites that are available and active, quite independent of the iron crystallite size