Fischer-Tropsch (FT) synthesis has been studied over a series of precipitated Fe catalysts promoted to investigate the effect of K and Cu promoters on the carbon number distribution of FT product. The main intention is to maximize the alpha-olefin selectivity by controlling the secondary reactions of alpha-olefin as a function of potassium and copper loadings. The results showed that impregnation of different loadings of Cu and K promoters to precipitated iron-based catalyst was found to have significant influences on the crystallographic structure, morphological and physical properties of iron-based catalysts, as well as catalytic activity, stability and selectivity performances during FT synthesis. 100Fe7Cu3K sample exhibited the highest catalytic activity and stability in TOS tests. The catalyst is capable of working under a variety of temperatures and space velocities at a same activity level with no significant activity loss. Proper control of Cu and K contents is essential to obtain maximum C-5+ yield since the changes in the relative loadings of both Cu and K promoters affect hydrocarbon product distribution. 100Fe7Cu3K sample has high secondary alpha-olefin hydrogenation activity as olefin/paraffin ratio decreases with increasing carbon number while C-19+ selectivity is relatively low compared to other samples. The effects of space velocity and temperature on alpha-olefin selectivity are strongly dependent on the amounts of Cu and K promoters and chain length. The maximum alpha-olefin/n-paraffin ratio has been obtained over 100Fe3Cu1K sample at 543 K with a space velocity of 3 NL/h/g-cat. (C) 2011 Elsevier B.V. All rights reserved.