Simulations of a bubbling/turbulent fluidized-bed reactor have been studied using the catalytic oxidation of n-butane to maleic anhydride (MAN) in the presence of a vanadium phosphorus oxide catalyst. The performance of the reactor was investigated using three different models:  (a) a simple two-phase flow model, (b) a dynamic two-phase structure model, and (c) a plug-flow model. The simple two-phase model was found to underpredict the performance of the fluidized-bed reactors because of the oversimplified assumptions involved in this model. By analyzing the mass transfer in the two-phase models, it was shown that the conversion of reactants occurs mainly in the emulsion phase at low gas velocities and in the bubble phase at high gas velocities. The performance of the reactor, in terms of n-butane conversion, yield of MAN, and selectivity of produced MAN, was analyzed at different superficial gas velocities, initial n-butane concentrations, and deactivation rates of the catalyst.