AN INFRARED STUDY OF THE DEHYDROGENATION OF ETHYLBENZENE TO STYRENE OVER IRON-BASED CATALYSTS

The dehydrogenation of ethylbenzene to styrene over unpromoted and potassium-promoted iron catalysts has been studied using kinetic measurements and infrared spectroscopy. Both the rate of styrene production and the activation energy for its formation are dependent on potassium content. The specific rate of styrene production is highest at approximately 10% potassium loading, while the apparent activation energy of the reaction is lowest at approximately 30% potassium content. The activity is significantly attenuated for potassium loadings in excess of 30%. Infrared spectra of the unpromoted and potassium-promoted catalyst surfaces after reaction indicate that potassium suppresses the extent of carbonaceous deposits, and that the active sites on both unpromoted and potassium-promoted catalysts are identical. Furthermore, although pure styrene adsorbed on unpromoted Fe2O3 is bound to the surface via the aromatic ring, with the vinyl group only slightly perturbed by interaction with the surface, the styrene product of ethylbenzene dehydrogenation binds to the catalyst surface through the vinyl group. (C) 1994 Academic Press, Inc.