Moessbauer spectroscopic study of phase conversions of an iron-containing oxide catalyst for oxidative dehydrogenation of butenes

Moessbauer spectroscopy was used to study the structure of ..gamma..-Al/sub 2/O/sub 3/-supported iron oxide, which is catalytically active in the oxidative dehydrogenation of butenes to divinyl. The phase conversions of the catalyst were investigated after treating it in reducing (butenes) and reaction (butenes + oxygen + water vapor) media and after regeneration in a stream of oxygen. It is shown that the supported phase changes from a structure similar to hematite (..cap alpha..-Fe/sub 2/O/sub 3/) to spinel structure both under the effect of butenes and the reaction mixture. When this happens ion exchange occurs between the spinel and the support, with the formation of partly hydrated complexes of Fe/sup 2 +/ ions in an asymmetric environment of O/sup 2 -/ ions and OH/sup -/ groups of the lattice of the support. These complexes vanish upon reoxidation of the catalyst, and part of the spinel is oxidized to hematite.