Co-2(CO)(8) supported on alumina pretreated at different temperatures was studied by temperature-programmed processes (temperature-programmed decomposition, TPDE; temperature-programmed oxidation, TPO; and temperature-programmed reduction, TPR). The gaseous decomposition and reaction products were analyzed by mass spectrometry and gas-phase IR spectroscopy. Oxygen and hydrogen consumptions by the surface species were followed with a TCD. The pretreatment of the support was found to affect the TPDE profile of cobalt carbonyls. CO ligands were removed more straightforwardly in the presence of OH groups producing a narrow TPDE profile. A broader TCD profile was found for the support with predominantly Lewis acid/base sites. The presence of OH groups also favored decomposition of surface cobalt carbonyl species, giving the lowest T-max. Oxidation and reduction of samples were observed to depend on the preceding treatment. Decarbonylation of the sample under inert gas intensified the interactions between cobalt and the surface, and the further reactivity of cobalt decreased. The cobalt species remained more active when decarbonylation was carried out under reactive gas. A Fischer-Tropsch reaction occurred when alumina-supported cobalt carbonyls were treated with hydrogen. The samples were active even at room temperature, producing methane, ethene, and methanol. The lack of CO ligands at higher temperatures prevented the formation of higher hydrocarbons.