Tentative explanation for the kinetic compensation effect in doped catalysts

The kinetic parameter compensation effect displayed by heterogeneous catalysts may occur when the global reaction is a combination of competing reactions which show the same mechanism and take place on different groups of active centres, each group showing different activation energy and pre-exponential factor values. In this study, a simple procedure is described for employing apparent kinetic data (ln(A) and Ea) that show a compensation effect in order to calculate the activation energies and preexponential factors (proportional to the population densities) of active centres that present equal reaction mechanisms in dual site catalysts. The procedure was used to reproduce apparent kinetic data taken from the literature and obtained from experiments with doped-catalysts prone to dual-site catalytic behaviour. The fittings obtained in all cases were very good. The population density of active centres with Ea2 activation energy showed constant growth with the increase in doping agent content, whereas that of the active centres originally present in the undoped catalysts (Ea1) showed varying trends.