Wustite phase transformations in iron catalysts for ammonia synthesis

The behaviour of wustite (ferrous oxide) during the catalyst preparation an d its activation process has been studied. The Mossbauer spectroscopy and X -ray diffraction have been used to follow wustite transformations. Inside t he wustite phase two different wustite structures were found - one attribut ed to the nonstoichiometric wustite and the second one, to the compound clo se to the "stoichiometric" FeO. The relative contents of both wustites depe nded on the cooling rate of the melted precursor. At the initial stage of a ctivation, at low temperatures, nonstoichiometric ferrous oxide was transfo rmed into magnetite and a compound closer to the stoichiometric FeO. The la st one decomposes further into magnetite and metallic iron. (C) 1999 Elsevi er Science Ltd. All rights reserved.