Dicobalt octacarbonyl, Co-2(CO)(8), was deposited on silica support pretreated at 300 degrees C, 500 degrees C and 600 degrees C, by vapour-phase adsorption at low temperature in a fluidized bed reactor. Adsorption of cobalt carbonyl on the silica surface and decarbonylation during heat treatment were followed by diffuse reflectance IR spectroscopy. The Co-2(CO)(8) rearranged to Co-4(CO)(12) and the surface was completely decarbonylated via subcarbonyl species. The decarbonylation of cobalt carbonyl on silica was also studied by temperature programmed reduction. Energy dispersive X-ray fluorescence was used to determine the cobalt content on the silica surface. Pretreatment temperature did not affect the saturation level of the cobalt carbonyl but influenced the hydrogen uptake of the non-decarbonylated samples in hydrogen chemisorption studies. Therefore, in gas phase preparation method the pretreatment temperature of the silica support could prove to be useful in the preparation of catalyst systems. A higher amount of cobalt on the support could be achieved through repetition of the deposition-decarbonylation sequence.