A study of low temperature catalytic combustion of methane has been performed in non-steady conditions, on Pd/Al2O3 and on Pd/TiO2, in the temperature range 240-340 degreesC, with the aim of clearing out the reaction mechanism and the differences induced by the two supports. Therefore the responses of reactants and products, above all at the beginning of the reaction (after the insertion of reactants in the carrier gas), have been followed, by using transient response method technique, in order to obtain information about the adsorptive properties of the fresh catalysts surface in reaction conditions. Since a complete view of the surface behaviour must include the knowledge of the surface features during the progress of the reaction, an isotopic transient analysis in steady conditions has been carried out by switching O-16(2) to O-18(2) in the reactants flow after having attained the stationary state of the reaction and by following the responses of labelled oxygen and carbon dioxide. The whole of these experiments allowed to gain a deeper insight in the activation of the C-H bonds and of active centres involved in this activation through various conditions of reactions, and to clear out that on titania supported catalysts there is a higher dispersion of palladium which compensate its lower surface area, and that carbonate surface species are the active sites during the steady progress of the reaction.