Using a kinetic equation derived from results obtained in a differential reactor, a grain model with variable properties was applied to calculate the global reaction rate for a particle. Furthermore, the theoretical model was developed to explain the performance of alumina as a catalyst for the Claus reaction at low temperature in an integral fixed bed reactor. The results were in good agreement with the experimental ones. The theoretical model was used to study the influence of the most significative parameters involved and to predict the catalyst performance in conditions of practical interest. It was shown that high H2S conversions and efficiencies of the catalyst were to be expected using highly porous materials and small particle sizes. These are the most important parameters for practical utilization.