STUDIES ON THE ISOMORPHOUS SUBSTITUTION OFFe(III) AND Cr(III) IN MCM-41 MOLECULAR SIEVES

Ferrisilicate and chromium silicalite with MCM-41 type structure have been synthesized and characterized using several spectroscopic techniques. The results of framework IR, ESR and solid-state MAS NMR measurements indicate an isomorphous substitution of Si4+ by iron or chromium ions in the silicalite framework. An absorption band at 960 cm-1 on the IR spectrum, characteristic of the incorporation in the case of titanosilicalites, is observed in both FeMCM-41 and CrMCM-41. Fe(III) and Cr(III) containing MCM-41 molecular sieves were also demonstrated by X-ray powder diffraction, SEM, UV-VIS, TG-DTA, NH3-TPD and chemical analysis. The experimental results indicate that the conceintion of Cr(III)incorporated into framework is lower than that of Fe(III) in silicalites.