MOSSBAUER SPECTROSCOPIC INVESTIGATIONS OF SUPPORTED IRON-OXIDE DEHYDROGENATION CATALYSTS

The characterization with Mossbauer absorption spectroscopy of support ed iron oxide-based catalysts, containing only iron oxide or containin g both iron oxide and potassium carbonate, after preparation as well a s after exposure to the reaction conditions used in I-butene dehydroge nation is described. The fresh catalysts all contain well-dispersed ir on(III) oxide particles. The potassium carbonate compound remaining on the surface after decomposition of KFeO2 formed during the calcinatio n step disperses the iron oxide phase in the case of the magnesia and zirconia supports. When using titania as a support the formation of a mixed oxide is observed. With the Fe/TiO2 catalyst FeTiO3 has been for med after dehydrogenation. In the Fe/MgO catalyst next to a surface-st abilized Fe1-xO phase, well-dispersed Fe3+ species are present. In the zirconia-supported sample Fe3O4 is detected. When both iron oxide and potassium carbonate are present, the iron-containing phase in the K,F e/MgO system also consists of a mixture of the Fe1-xO phase and well-d ispersed Fe3+ species. In the K,Fe/ZrO2 catalyst besides the Fe3O4 pha se a well-dispersed Fe3+ species is observed. However, the magnetite c rystallites in this catalyst are notably smaller than in the Fe/ZrO2 c atalyst after dehydrogenation. No distinction between a well-dispersed (alpha)Fe2O3 or a well-dispersed KFeO2 phase can be made at this stag e. It is most probable that the main functions of the potassium in the supported catalysts can be described as, firstly, dispersing the iron phase, and secondly, providing the, gasifying properties required for the auto-regenerative character of the catalyst.