MOSSBAUER SPECTROSCOPIC STUDIES OF FE(II)-Y, FE(II)-MORDENITE, AND FE(II)-ZSM-5 ZEOLITES

Mossbauer spectroscopy was used to study the room temperature adsorption of dioxygen and carbon dioxide on a high Si/Al ratio Fe(II)-Y zeolite and of carbon monoxide on Fe-mordenite and Fe-ZSM-5. All of these adsorbates were found to interact with cations that contribute Fe(II) doublets with small splittings to the spectra. In each case, the adsorption process increased the coordination of the cations, decreasing the spectral area of the Fe(II) inner doublet and forming a new doublet with a larger quadrupole splitting. The adsorption of CO on Fe-mordenite and Fe-ZSM-5 removed the inner doublet completely, whereas the same adsorbate does this only partially for Fe(II)-Y. The assignments made for the two doublets present in the spectra of these zeolites were tested theoretically. The calculations suggested that the differences in Mossbauer spectroscopy parameters of cations giving the two doublets may arise from differences in the length and degree of covalency of Fe-O bonds in the two types of coordination.