POLARIZABILITY MODEL OF ACIDITY OF ZEOLITES

A new model has been developed for the estimation of structural acidit y parameters and the acid amount of zeolites using valence electron de nsity, atomic polarizability, and chemical composition. Based on this model, the computed zeolite acidity has been compared with the data ob tainable from Sanderson's electronegativity model and also with availa ble experimental data. The general agreement between our calculated va lues and those reported in the literature has been found to be very go od in the case of mordenites. It has been established that electronega tivity equalization (EE(q)) in zeolites could be equally explained via the electronic polarization process governed by the proposed equation : EE(q) = 1.67 alpha(p))(N-Q/alpha(Q))(N-R/alpha(R))](1/(p+q+r)), wher e N is the valence electron density and a the atomic polarizabilities of the constituting atoms expressed in the unit of volume, and p, q, r are the number of atoms representing a molecule of general formula P( p)O(q)R(r). The relative polarizing power of structures has also been reported as a function of Al content. This means that increased bond p olarization will result in enhanced acidic behavior of the protons upo n interaction with basic substrate molecule. This is why relative pola rizing powers, alpha'(p), are directly related to the Al content, the acidity [H+], and shrinkage effect of bond lengths (D-t-0).