Reduced iron sites in Fe–BEA and Fe–ZSM-5 zeolites: FTIR study of CO adsorption and 12C16O–13C18O co-adsorption

Accessible iron in oxidized Fe–ZSM-5 and Fe–BEA zeolites is mainly in the form of Fe3+ species that do not interact with CO. Some exchanged cations are stabilized as Fe2+ species and form carbonyls detected in the 2205–2190 cm−1 region. Evacuation of the samples at 673 K provokes autoreduction of part of Fe3+ and creation of more Fe2+ sites detectable by CO. Reduction of the samples with CO at 673 K leads to a significant increase of the number of Fe2+ sites and creation of new reduced iron sites (supposed to be Fe+ cations). With CO the latter forms tri- and tetra-carbonyl complexes. In order to clarify the structure of these species, adsorption of CO isotopic mixtures is studied. It is demonstrated that the use of 12C16O–13C18O mixture provided a better resolution of the carbonyl bands as compared to the conventional 12C16O–13C16O mixture.

We report on the FTIR observation of new tri- and tetra-carbonyl complexes produced with reduced iron sites in zeolites. In order to clarify the structure of the polycarbonyls, adsorption of CO isotopic mixtures was studied. It was demonstrated that the use of 12C16O–13C18O mixture provided a better resolution of the carbonyl bands as compared to the conventional 12C16O–13C16O mixture.Figure optionsDownload high-quality image (116 K)Download as PowerPoint slide