Isomorphic substitution of heteroatoms for Y zeolite in aqueous solns. of NH4BF4, (NH4)ZrF7, (NH4)TiF6, (NH4)FeF6, and CrF3.3NH4F was studied. All the heteroatoms except B are substituted into the zeolite framework, and the extent of substitution is in the order Fe > Ti > Cr u Zr. The heteroatom substituted Y zeolites are analyzed and characterized by x-ray diffraction, IR, and DTA methods, showing that the heteroatoms are located in the zeolite framework. In terms of the isomorphic substitution the mechanism, the main factors affecting the substitution are discussed. The feasibility and the extent of isomorphic substitution of a heteroatom in aqueous solution of a fluorocomplex can be predicted from the ionic radius of the heteroatom, the cumulative stability constants of the fluorocomplex, the hydrolysis equilibrium constant of the metal cation, and polymerisation equilibrium constant of the metal hydroxide.

Key words: INFRARED SPECTROPHOTOMETRY, ZEOLITE, X-RAY DIFFRACTION ANALYSIS, DIFFERENTIAL SCANNING CALORIMETRY, AMMONIUM FLRORIDE, CHROMIC FLUORIDE