The influence of isomorphous substitution on the cation distribution in faujasite-type zeolites; The structures of dehydrated Na-LZ210 and hydrated KGaY

Abstract

The structures of dehydrated Na-exchanged LZ210 ( Si Al = 4.8; 623 K) and of hydrated KGaY zeolites were determined using X-ray powder diffraction methods. The changed distribution relating to Y-zeolites, reflects the framework-cation interaction energies, which are due to a change in the Si/Al ratio (NaLZ210) or to a substitution of the aluminum ions for gallium ions (KGaY). For dehydrated Na-exchanged faujasite-type zeolites, the site preferences are: I > II > I' (high aluminum content, J. phys. Chem. 92, 6747, 1988); II > I' > I (low aluminum content). Based on a previously determined statistical thermodynamical model ( J. phys. Chem. 92, 6740, 1988), it can be inferred that the cation distribution at high cation loadings is largely determined by the interaction energy of the cations on adjacent sites I and I'. All available literature data on dehydrated sodium-exchanged faujasite-type structures are rationalized on the basis of this model, and energy level differences as well as interaction energies are fitted. Isomorphous substitution of Al by Ga reduces the framework-cation interaction energy, which may be explained by a higher covalency of the framework.