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Abstract:
Solid-state ion-exchange reactions proceeding upon grinding of hydrated NH4-Y zeolite and FeCl2·4H2O in air and subsequent heating in vacuum have been followed by X-ray diffraction (XRD) and temperature-programmed evolution of volatile reaction products (H2O, NH3 and HCl) monitored by mass spectrometry (MS). Changes in valence state and coordination environment of the exchanged iron ions upon heat treatment up to 720 K in vacuum and air, as well as in hydrogen after treatment in air, were studied by Mössbauer spectroscopy. Partial ion exchange and oxidation to cationic hydroxy-iron(III) species proceed upon mere grinding. Heat treatment in vacuum results in partial autoreduction and characteristic environmental changes of di- and tri-valent Fe species, especially in the temperature range between 620 and 720 K. In an oxidizing atmosphere, autoreduction is suppressed; however, at temperatures >520 K, iron(III) oxide is formed in increasing amounts. Reduction by hydrogen subsequent to heat treatment in air at 720 K results in the formation of a magnetite-like oxide phase and some metallic α-iron.
