Self-diffusion of various cations in natural mordenite

Abstract

The self-diffusion of various cations in hydrated natural mordenite has been studied. From the variation of the self-diffusion coefficient D^* with temperature, the energy of activation E and the pre-exponential factor D₀ for the self-diffusion process have been calculated from the Arrhenius equation D^*=D₀ exp (E/RT). The values of D^*, D₀ and E have been found to exhibit peculiarities which were not so evident in studies with analcite¹ and chabazite,² two zeolites which have simpler channel structures. Only limited exchange of the divalent ions Ca²⁺, Sr²⁺ and Ba²⁺ with the sodium form of the exchanger could be achieved. These divalent-ion self-diffusion studies exhibited unusual features and the interpretation of the results was complicated by the unknown effect of the sodium ions present in the lattice. These studies have shown, however, that much insight of the motion of ions in these zeolite channels can be obtained from kinetic measurements.