STRUCTURE OF FE-K MIXED-OXIDE CATALYSTS UNDER THE REACTION CONDITIONS OF ETHYLBENZENE DEHYDROGENATION

The formation and the stability of Fe-K double oxides have been examined to study the active component in the dehydrogenation catalysts consisting of Fe2O3 and K2CO3 using for styrene synthesis. Although formation of KFeO2 and K2O . nFe2O3 was observed by solid state reaction of Fe2O3 and K2CO3 at 900-degrees-C, only KFeO2 was found in the reaction at 750-degrees-C. Addition of K2CO3 to Fe2O3 improved the catalytic activity and selectivity significantly, independent of the amount of K2CO3. The surface composition of Fe-K oxides calcined at 750-degrees-C was measured by XPS, and the surface seemed to be covered by KFeO2. The stability of KFeO2 was examined in different atmosphere, and it decomposed in CO2 at the temperature of dehydrogenation reaction. However it remained stable after the reaction, although CO2 was present in the reactor. We tried to measure the equilibrium pressure of CO2 (P(CO2)) which was evolved by the solid state reaction of Fe2O3 and K2CO3 to form KFeO2. We found that in typical reaction conditions P(CO2) was less than equilibrium, and so KFeO2 was stable in it. By addition of CO2 in the reactor, the catalytic activity and selectivity rapidly dropped when P(CO2) was higher than equilibrium pressure, but stayed constant when P(CO2) was less than equilibrium pressure. Thus we finally concluded that KFeO2 is the active component in the dehydrogenation catalysts consisting of Fe2O3 and K2CO3.