ISOMORPHOUS SUBSTITUTION OF IRON IN THE FRAMEWORK OF ZEOLITE ZSM-23

A crystalline ferrisilicate having the framework structure of ZSM-23 zeolite has been synthesized and characterized. The presence of iron in the zeolite lattice framework has been confirmed by spectroscopic (XRD, framework IR, ESR, and XPS), DTA/TG, magnetic susceptibility, ion exchange, and catalytic activity results. Chemical analysis and XPS show the absence of any significant quantity of Al(SiO2/Al2O3 > 1400) in the ferrisilicate. XRD patterns of the as-synthesized as well as the calcined Fe/ZSM-23 matched well with that of ZSM-23 (MTT topology). Framework IR bands of ZSM-23 are shifted toward lower frequencies on incorporation of iron in the framework. The white color of the as-synthesized as well as that of calcined samples of Fe/ZSM-23, ESR (g = 4.4), and magnetic susceptibility (μ = 5.4-5.8, BM) data indicate that FeOFe interactions (due to oxides of iron like Fe2O3 or Fe3O4) are absent, and that well dispersed Fe 31 ions are present in a magnetically dilute environment. Fe/ZSM-23 exhibits significant ion exchange capacity and catalytic activity/shape selectivity in the metaxylene isomerization reaction. Fe2+ ions in zeolite lattice positions account for the ion exchange capacity and shape selective catalytic activity of this crystalline ferrisilicate. © 1990.