Mössbauer study of iron-containing zeolites

Abstract

Metal-loaded zeolites combine the advantages of shape selectivity and high metal dispersion and have therefore been investigated from the point of view of their catalytic performance, especially for hydrogenation and Fischer–Tropsch synthesis. In the case of iron, Mössbauer spectroscopy offers a valuable means for the characterization of the electronic and chemical structure arising from the interaction between a metal ion and a solid electrolyte and also allows a quantitative determination of exchange-site population.

In this paper comparative Mössbauer studies of ⁵⁷Fe on various zeolites starting from different precursors are presented with the aim of selectively controlling the location of the metal ion or complex in the exchange sites.

Complex ions of the type [FeL₃]²⁺ with L = 1,10-phenanthroline or 2,2′-dipyridyl have been exchanged in X- and Y-zeolites and the evolution with thermal treatment under vacuum of the exchange-site population has been investigated. An attempt has also been made to define better the exchange sites for Fe²⁺ in the particular structure of zeolite ZSM-5.