LaCoO3, LaMnO3, La0.8Sr0.2CoO3, and La0.8Sr0.2MnO3 perovskites have been used for the combustion of VOCs (toluene and methyl-ethyl-ketone) in air, at temperatures between 200 and 300 degrees C. Reaction tests have been carried out using the single compounds, as well as binary mixtures in different proportions. Several characterization techniques have been employed in order to gain insight into the changes taking place on the catalyst surface, especially during the combustion of binary mixtures. The discussion attempts to relate these changes to the catalytic performance observed.