The decomposition of toluene on gamma-alumina, MnO2-alumina and Ag2O-alumina catalysts in a plasm a-catalytic reactor is tested. A comparison between catalytic, catalyst-after-plasma and catalyst-in-plasma systems is made in 150-400 degrees C temperature range. An Arrhenius plot is made in order to deduce the mechanism of plasma activation. It was found that there is no difference between the measured activation energy for catalytic and catalyst-after-plasma systems. On the other hand it was found that plasma could activate catalyst placed inside of the discharge. Plasma treatment decreases the activation energy for the silver-alumina catalyst but does not increase the number of active centers on the surface of Ag2O-alumina. In case of MnO2-alumina, the activation mechanism is different: plasma does not change the activation energy and but does increase its efficiency due to formation of additional active centers. The mechanism of catalyst activation in plasma, which includes the structural change of manganese ions, is suggested.