The selective oxidation and ammoxidation of hydrocarbons in fixed-bed or fluidized-bed reactors is conventionally characterized by the simultaneous presence of oxygen gas and hydrocarbon vapor at the active sites of the catalyst. In order to increase the selectivity it has been suggested (Sze and Gelbein, 1976; Contractor and Sleight, 1987; Contractor, 1988) to separate the reaction into two parts; i.e. a first step where the catalyst chemisorbs oxygen and a second step, where the oxidized catalyst reacts with the hydrocarbons. In the present work this concept has been tested on the laboratory scale. The oxidation of n-butane to maleic anhydride (MA) has been taken as an example. The reaction step was carried out in a riser of a circulating fluidized bed, the solids return line of which was used to implement a regenerator fluidized bed for the reoxidation step. A model of this reactor has been developed which takes the oxygen loading on the catalyst particles into account. Scale up calculations show that high solids circulation rates are necessary which, in turn, demand a high attrition-resistance of the catalyst.