The relative stability of zeolite frameworks

The question is examd. as to whether there is a theor. basis to an apparent relation that has been exptl. obsd. between the lattice topol. and the Al/Si ratio of zeolites. Calcns. are presented for 3 lattices formed with different Al/Si ratios, faujasite, mordenite, and ZSM-5. The relative stabilities of these lattices were studied as a function of Al/Si ratio in the presence or absence of adsorbed water. The Na+ are taken as the compensating ions. Two contrasting techniques, lattice energy minimization and extended Hueckel theory, were used. The energy differences of Al-free lattices are very small (.apprx.10 kH) and tend to decrease function of Al content. Wide pore zeolites tend to become stabilized with respect to medium pore zeolites at high Al conten