Synthesis of Fe-MFI zeolites in fluoride-containing media

Abstract

As many as three Fe/u.c. were introduced into the MFI framework in a fluoride-containing medium. Initial gels of the composition 10SiO 2: xFe(NO 3) 39H 2O: yMF:1.25TPABr:300H 2O (where M=NH 4, Na, K, Cs, x=0.1, 0.2 and 0.3, and y=3, 6, 9, 12, 15, 18, 21 and 24, TPABr=tetrapropylammonium bromide) were heated under hydrothermal conditions at 170 °C. NH 4- and Cs-containing systems are most effective in the incorporation of Fe into the framework. The location of iron on tetrahedral framework positions is indicated by both the white color of the samples and the isomer shift in the Mössbauer spectra (IS<0.3 mm/s). During calcination, some framework Fe atoms leave the framework. The crystallization patterns and crystal morphologies are influenced by the fluoride salt added to the reaction mixture. Kinetic data show that the cations exert specific forces on the stabilization of the crystals under development.