High quality transportation fuels for engine are certain distillates with C5+ hydrocarbons. A promising method to produce them from other resources than petroleum is the Fischer-Tropsch synthesis (FS) process which gives product with a wide range of boiling point. The present authors have investigated FTS by simultaneously developing a graphite supported iron based catalyst. Results indicate that a suitable amount of potassium added to the graphite-supported catalyst promoted the reduction behavior and enhanced the selectivity to liquid hydrocarbons significantly. Products were mainly composed of C-4-C-10 alpha-olefins with little methane, whose distributions changed with time on stream. The alpha-olefins in the liquid phase reaction media promoted the selectivity of C5+ distillate up to near 90% and while suppressing the formation of lighter hydrocarbons with higher CO conversion. A reaction network involving the secondary reactions of alpha-olefins was proposed. (C) 2015 Elsevier B.V. All rights reserved.