The Fischer-Tropsch synthesis of lower olefins (FTO) is an alternative process for the production of major chemical building blocks from natural gas, coal, or biomass-derived synthesis gas. The addition of low concentrations of sulfur plus sodium to Fe/alpha-Al2O3 resulted in catalysts with high C-2-C-4 olefins selectivity (similar to 50%C), enhanced catalytic activity, and decreased methane production (<20%C) when the reaction was carried out at 340 degrees C, 20 bar and H-2/CO = 1. Sodium reduced methane selectivity by increasing the chain growth probability while sulfur probably reduced the hydrogen coverage of the catalyst resulting in even lower methane selectivities and higher olefin content of the products. The addition of extra sodium resulted in a detrimental effect on catalytic activity while favoring the formation of carbon deposits. Our results show that the nature and concentration of the promoters play a key role in the design of FTO catalysts with optimum catalytic performance. (c) 2013 Elsevier Inc. All rights reserved.