Abstract: The substitutions of Ti, Fe and Zr into zeolite Yin the aqueous solutions of (NH₄)₂TiF₆, (NH₄)₃ZrF₇ and (NH₄)₃FeF₆ were systematically Investigated. It was found that Ai atoms in the framework can be replaced by some metallic elements and the extent of substitution depends on the M/A1 ratio of the solution. The maximum allowable M/A1 ratio of the aqueous solution Is related with the radius of the Matom and the stability constant of the MF_n^m- complex. The substituted zeolite samples with crystallinity greater than 80% were characterized by means of XRD, IR, DTA, TPRand NH₃-TPDmeasurements. The incorporation of Ti, Fe and Zr into the zeolite leads to an increase in the unit cell parameter, a lowering of thermal stability and a red shift of the asymmetric stretching frequency. The extent of these changes is apparently related with the ionic radius of the metallic element and the degree of substitution. The results of various characterization methods show that the het-eroatoms are readily Introduced into the zeolite framework by this preparation method. It was also observed that the substitution of heteroatoms may strengthen or weaken the surface acidity of zeolite Y.

Key words: Isomorphous substitution, Zeolite Y, Crystallinity, Unit cell parameter