In this paper, we study the control of a fixed catalyst multi-staged reactor. This reactor is an industrial one, used for sulphur dioxide oxidation. The aim of this work is to determine the best control strategy between one whom consist to control the production capacity of the reactor and another, more usual, whom consist to control the maximal catalyst temperature in order to avoid the occurrence of hot spot inside the catalyst. Command algorithm used is the generalised predictive control (GPC) with on line process identification. The results obtained by numerical simulation show that the control of the production capacity is possible and also preferable, since the reactor is strongly influenced by inlet reagent concentrations and, on the other hand, it presents a notable thermal stability conferred by the thermal inertia due to the important catalyst mass.