A temporal analysis of products (TAP) set-up was applied to investigate the initial elementary steps of the Fischer-Tropsch synthesis over silica-supported cobalt catalysts, i.e., hydrogen and carbon monoxide adsorption. Single-pulse TAP experiments were performed over both reduced and passivated catalysts in order to qualitatively and quantitatively assess the mechanism and kinetics of H-2 and CO adsorption. Multi-pulse experiments were performed to change the state of the catalyst in a predefined way. Only fast and equilibrated physical hydrogen adsorption was observed over a passivated silica-supported cobalt catalyst. Over the reduced catalyst, the surface sites exhibited significant heterogeneity for adsorption. TAP responses were successfully described assuming two different reversible adsorption processes for hydrogen and both irreversible and reversible adsorption for carbon monoxide. Supporting qualitative information about reversibility of the adsorption was also obtained through alternating pulse experiments. (C) 2009 Elsevier B.V. All rights reserved.