Aluminum distribution in mordenite-zeolite framework: A new outlook based on density functional theory calculations

Abstract On the basis of the density functional theory (DFT) calculations, the successive isomorphic substitution of one to six tetrahedrally coordinated Si cations by trivalent Al was systematically studied. As a result of exploring a significant number of configurations, without using a priori assumptions, it was found that the Al atoms are accommodated according to the ground state sequence in the tetrahedral sites TI − TIII − TIII − TI − TIII − TIII. The results in the general show: a) Al cations preferentially occupy TIII positions, b) the distribution of cations in the framework does not violate Lowenstein’s rule, c) the distribution of cations in the framework does not satisfy Dempsey’s rule, and d) only one Al cation is found per ζ-cage.