The behavior of iron oxide-based catalysts supported on zirconia in the dehydrogenation of 1-butene was investigated, Iron oxide-on-zirconia catalysts deactivate during operation due to carbon deposition, It was shown with XRD that solid state reactions between the active phase and the support do not take place in the zirconia-supported catalysts : the iron-containing phase after reaction is Fe3O4. The total amount of carbon deposited onto zirconia-supported catalysts containing only iron oxide as determined with temperature-programmed oxidation is about 2 wt% C after 20 h. It was also shown that a carbon species deposited in narrow pores was present in iron oxide-on-zirconia catalysts, The KFe/ZrO2 catalysts proved to be more stable than KFe/MgO catalysts : for catalysts containing highly dispersed iron oxide only a slight deactivation was observed after about 100 h on stream, This deactivation is attributed to migration of potassium from the catalyst to the quartz reactor, Catalysts of low loadings (1 wt% Fe, 1 wt% K) or with less well-dispersed iron oxide deactivate in a shorter period of time : an incomplete coverage of the zirconia support leads to deactivation by carbon deposition. The selectivity to butadiene of the KFe/ZrO2 catalysts is about 60%, which is related to a high production of CO2. This is attributed to carbon deposition taking place in the small pores of the zirconia-supported catalysts, The coke is subsequently gasified, probably by the supported potassium carbonate. Eliminating the small pores substantially improved the butadiene selectivity.