A promising way to create supported metal oxide catalysts consists of the irreversible adsorption of metal acetylacetonate complexes on an oxide support and the subsequent thermolysis of the metal complexes. This study focuses on the adsorption and thermolysis of vanadyl acetylacetonate (VO(acac)(2)) on both silica and alumina supports and investigates how the thermal decomposition of the supported complex influences the final catalytic activity of the VOx monolayer. The supported complex was subjected to thermal treatment both in vacuum and in ambient air and was analyzed in situ by infrared spectroscopy and thermogravimetry. The adsorbed complex is very stable in vacuum conditions. A very distinct VOH vibration was observed during the thermolysis in air of the silica-supported complex, and intermediate acetate species were observed for the alumina-supported complex.