IRON-BASED DEHYDROGENATION CATALYSTS SUPPORTED ON ZIRCONIA .2. THE BEHAVIOR IN THE DEHYDROGENATION OF 1-BUTENE

The behavior of iron oxide-based catalysts supported on zirconia in th e dehydrogenation of 1-butene was investigated, Iron oxide-on-zirconia catalysts deactivate during operation due to carbon deposition, It wa s shown with XRD that solid state reactions between the active phase a nd 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 ir on 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 K Fe/ZrO2 catalysts proved to be more stable than KFe/MgO catalysts: for catalysts containing highly dispersed iron oxide only a slight deacti vation was observed after about 100 h on stream, This deactivation is attributed to migration of potassium from the catalyst to the quartz r eactor, Catalysts of low loadings (1 wt% Fe, 1 wt% K) or with less wel l-dispersed iron oxide deactivate in a shorter period of time: an inco mplete coverage of the zirconia support leads to deactivation by carbo n deposition. The selectivity to butadiene of the KFe/ZrO2 catalysts i s about 60%, which is related to a high production of CO2. This is att ributed to carbon deposition taking place in the small pores of the zi rconia-supported catalysts, The coke is subsequently gasified, probabl y by the supported potassium carbonate. Eliminating the small pores su bstantially improved the butadiene selectivity. (C) 1996 Academic Pres s, Inc.