High surface area MCM-41 with mesoporous structure and conventional SiO 2, containing micropores were used as support materials for Co 2 (CO) 8 in a gas phase preparation of supported cobalt samples. Two different kinds of preparation methods were used: direct deposition, with continuous adsorption of cobalt carbonyl on to the support over an extended period of time; and a pulsing method with successive deposition/decarbonylation cycles. Since the reduced metal is usually the active phase in catalytic reactions, the aim of the preparation of heterogeneous catalysts is to produce samples in which the supported metal is easily reducible. The effects of the support materials, the gas phase deposition methods and decarbonylation atmospheres on the reactivity of the Co/SiO 2 and Co/MCM-41 samples toward oxygen and hydrogen treatments were compared. According to the results, reducibility of the samples decreased in the order: MCM-41+pulsing method > SiO 2 +pulsing method > SiO 2 + direct method > MCM-41 + direct method. Oxygen/hydrogen consumptions of the samples decreased in the decarbonylation atmosphere inert > oxidising > reducing. Co/SiO 2 and Co/MCM-41 samples prepared via pulsing method indicated a good stability during oxidation/reduction treatments.