An investigation was undertaken to evaluate the intrinsic reactivity, stability and associated diffusional parameters of catalyst pellets consisting of platinum and palladium on rutile for the conversion of sulphur trioxide to sulphur dioxide. This catalyst was prepared by the sintering at 1103 K of a catalyst preparation consisting of 0.5 wt% platinum and 0.5 wt% palladium on mainly anatase (TiO2) and the experimentation was carried out with a micro pellet reactor. A three dimensional heterogeneous model was generated for the reaction in the micro pellet reactor with five cylindrical pellets and solved using a CFD software code. A reversible reaction rate for the reaction was found to be applicable and the catalyst was found to reach a constant activity within an acceptable time period after start-up. Arrhenius parameters (reaction rate) were evaluated for the catalyst pellets and an overall kinetic model for the catalyst pellets suitable for designing fixed bed reactors was validated. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.