Structural changes in FeO_x/γ-Al₂O₃ catalysts during ethylbenzene dehydrogenation

The structural changes that occur in a FeO_x/γ-Al₂O₃ catalyst during the dehydrogenation of ethylbenzene in a fluidized CREC Riser Simulator have been investigated. Chemical and morphological changes are observed to take place as a result of reaction. Electron microscopy reveals the formation of needle-like alumina structures apparently enclosing iron oxide particles. The formation of such structures at relatively low temperatures is unexpected and has not previously been reported. Additionally, X-ray diffraction and Mössbauer spectroscopy confirmed the reduction of the oxidation state of iron, from Fe₂O₃ (haematite) to Fe₃O₄ (magnetite). Iron carbides, Fe₃C and ɛ-Fe₂C, were detected by electron microscopy through electron diffraction and lattice fringes analysis. Carbon deposition (coking) on the catalyst surface also occurs. The observed structural changes are likely to be closely correlated with the catalytic properties of the materials, in particular with catalyst deactivation, and thereby provide important avenues for future study of this industrially important reaction.