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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 KFeO₂ supported on a solid solution of K₂Fe₂₂O₃₄ in Fe₃O₄. The ternary K₂Fe₂₂O₃₄ 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 Fe³⁺ 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 KFeO₂ was confirmed by independent synthesis of this phase and comparison of its catalytic activity with that of the technical catalyst.