Comparison of the structural properties of isomorphously substituted Fe in mordenite zeolites prepared by different methods

摘要

Fe was introduced in mordenite zeolite by means of ion exchange either in solid or in liquid state The iron loading (50-200 wt%) iron precursos (FeSO_4 7H_2O and FeCl_3) and mordenite starting material (NH_4M HM and NaM) were varied during the exchange processes The Fe species were characterized by N_2 adsorption measurements as well as by XRD and mossbauer spectoscopies The Fe-mordenite samples prepared by liquid-state ion exchange attainee remarkable Fe dispersion and surface areas higher than those of the parent It was found that Fe~3+ ions which substituted the framework Al and accordingly occupied tetrahedarl sites were decreased with Fe loadings with concomitant increase in Fe~3+ -occupied octahedral sites The lateer sites disappered at 20 K to provoke the superparamagntice a-Fe_2O_3 in different particles size The acid leaching (0.1 M HCl 333 K 3 h) of the samples showed the disappearance to fthe most highly distorted extra-framework Fe~3+ species providing an inditattion of theri presene on the external surfade On the other hand a hematite phase was detected in the solid-state ion exhange of FeCl_3 with either HM or MH_4M at the loading of 100% Fe More correlations between Mossbauer daa on one hand and XRD and texturing properties on the other hand were evaluated and discussed.