Study of the Ferzeolite-L system Part I: Characterization of iron species and their structural properties

Abstract

The chemisorption properties of two solids, called Fe/ZLK and Fe/ZLH were studied. The samples were obtained by dry impregnation of potassic and acidic forms of zeolite-L with a ferric salt, as described in Part I. The adsorption isotherms of CO at 193 K and H2 at 673 K were measured. “In situ” Mössbauer spectroscopy (MS) at 298 and 193 K of the reduced solids with chemisorbed CO allowed to confirm the preferential location of the Fe2+ exchanged with the support in both samples, in agreement with that obtained in Part I: sites D for Fe/ZLK and sites A for Fe/ZLH. The CO chemisorption resulted in an inappropriate method to obtain the metallic area of reduced Fe/ZLK, since Fe2+ ions in sites D also chemisorb CO with a 1:2=Fe2+:CO stoichiometry. In order to obtain the amount of Fe0 surface atoms, H2 chemisorption at 673 K in 10–80 Torr pressure range was successfully used. Combining this technique with MS, it was possible to determine the values of the Fe0 crystal diameters.