The CO hydrogenation reactions over un-promoted and alkali (Li, Na, K and Rb) promoted iron-based catalysts were studied by pulsing CO method. The pulse experiments indicate that alkali metals suppress the CO hydrogenation or conversion and the methane formation. Through analyzing the data, it is found that alkali promoters decrease the surface concentration of hydrogen, improve the CO adsorption and increase the retention time of carbon species on the catalyst surface in the turn of Li, Na, K, Rb. These promotional effects well explain the hydrocarbon product variation over different alkali promoted catalysts in Fischer-Tropsch synthesis. (C) 2014 Elsevier B.V. All rights reserved.