Solid-state ion exchange in zeolites. Part 5.—NH4-Y–iron(II) chloride

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.