Thermal desorption of potassium ions and atoms from K-doped iron oxides (Fe3O4, Fe2O3) and potassium ferrites (KFeO2, K2Fe22O34) that are the principal phases of the iron oxide catalysts for dehydrogenetion of ethylbenzene to styrene was investigated. From the Arrhenius plots the activation energies for desorption of K and K+ were determined in the process temperature range for each of the phases. Based on these results the desorption energies obtained previously for the commercial styrene catalysts were reinterpreted and the K storage and release phases were explicitly identified. The results were discussed in terms of a surface stability diagram. It was shown that in the active state of the catalyst the K2Fe22O34 component is responsible for excessive potassium release. The proposed optimal morphology of the catalyst grain consists of a core K2Fe22O34 surrounded by a compact shell of active KFeO2, while a core and cracked-shell model was adapted to account for the potassium desorption data from the real catalysts.