The effect of long lasting action of reagents in the process of catalytic oxidation on the oxide catalyst was investigated. Pure V2O5 was selected to test the reaction of SO2 oxidation. It has been stated that degree of catalyst deactivation was dependent on the gas composition and temperature. The apparent energy of activation was determined. Its value depends on the gas composition what proves that those gases modify the catalyst surface. During long-lasting action of air the apparent energy of activation remains constant. However, it varies if mixture of air and SO2 is applied.