Isomorphous substitution of Fe 3 + in the framework of aluminosilicate mordenite by hydrothermal synthesis

Abstract

Fe 3+ framework-substituted mordenites have been hydrothermally synthesized under template-free conditions using the gel compositions with SiO 2/(Al 2O 3 +Fe 2O 3) molar ratio of 20, 15 and 10 where Fe 2O 3/Al 2O 3 molar ratio was varied from 0 to 1000. Crystalline materials with Fe incorporated into the framework have been obtained from starting gels containing up to 0.5, 0.63 and 0.75 mol fraction of Al 2O 3 replaced by Fe 2O 3 at SiO 2/ (Al 2O 3 +Fe 2O 3) ratio of 20, 15 and 10, respectively. Using gels with lower SiO 2/(Al 2O 3 + Fe 2O 3) ratio has extended the maximum substitution level of Fe for Al. XRD, UV visible, IR spectroscopy and chemical analysis have provided evidence for the presence of framework Fe. When Al atoms were gradually replaced by Fe. unit cell parameters increased and an asymmetric stretching vibration of Si-O-T was shifted to lower wavenumbers. A new band around 3630 cm −1 due to Si(OH)Fe groups observed in the IR spectra of Fe-containing mordenite also supports the framework incorporation of Fe.