Crystallographic study of the distribution of cations in Y-type zeolites containing FeII and FeIII

Abstract

X-ray powder diffraction has been utilized to determine the location and coordination environment of iron cations in Y-type zeolites after a variety of pretreatment procedures. The iron is introduced by an anaerobic ion-exchange technique with the Fe^II cation. The exchange level in all samples is ca. 45%. After dehydration of Fe^IIY samples, the iron cations are found in six-fold coordination at site I and in three-fold coordination at site I′. Upon oxidation to Fe^III, most of the iron migrates out of the hexagonal prism (site I) and can be localized at site I′. No evidence for oxide-bridged complexes was found in any of these samples. The zeolite lattice is unstable toward high-temperature oxidation of the Fe^II to Fe^III as partial framework decomposition is observed. In all dehydrated samples, the precipitation of amorphous iron oxides is indicated.