FE IN MFI METALLOSILICATES, CHARACTERIZATION AND CATALYTIC ACTIVITY

Fe was introduced in MFI molecular sieves by four means: direct synthe sis, postsynthetic modification of boralite, ion exchange with HZSM-5 in solid or liquid state, and by impregnation. Fe species were charact erized by TPR and EPR (dispersed Fe3+). Additional information was obt ained from the FTIR spectra of adsorbed acetonitrile-d(3) and from TPD of ammonia, both of which characterized the acidity of the samples em ployed. The catalytic activity was examined in oxidative dehydrogenati on of ethane, in aromatization of ethane and ethene, in CO oxidation b y O-18(2) and in O-18(2) + O-16(2) reactions. The results obtained wer e compared with those over Ga metallosilicates: it was found that Fe i n the zeolite framework appeared only in directly synthesized samples. These were much more active in oxidative dehydrogenation of ethane th an HGaZSM-5, but much less active in the aromatization reactions. The oxidation of CO with gaseous oxygen began < 100 degrees C, contrary to Ga samples over which the onset of reaction needed a much higher temp erature. Significant activation of oxygen molecules, leading to the eq uilibration of gaseous oxygen molecules as well as to the exchange wit h lattice oxygens, was observed at 400 degrees C over the most active ferrisilicate. (C) 1998 Elsevier Science B.V.