The nature of the iron oxide-based catalyst for dehydrogenation of ethylbenzene to styrene: I. Solid-state chemistry and bulk characterization

Abstract

The active catalyst for the dehydrogenation of ethylbenzene is generated from a precursor material consisting of hematite and potassium hydroxide (with additional promotors) during the initial phase of catalyst operation at 873 K in a steam atmosphere. The active phase is a thin layer of KFeO 2 supported on a solid solution of K 2Fe 22O 34 in Fe 3O 4. The ternary K 2Fe 22O 34 phase acts as storage medium from which the active surface is continuously supplied with a near-monolayer coverage of potassium ions in an environment of Fe 3+ ions. The catalyst undergoes a continuous solid-state transformation caused by the migration of potassium ions. This requires a certain degree of imperfection in the matrix lattice which originates from the catalyst preparation and from the addition of promotors which act on the iron oxide lattice rather than on the surface chemistry. The identity of the active phase with KFeO 2 was confirmed by independent synthesis of this phase and comparison of its catalytic activity with that of the technical catalyst.