To investigate the effect of hydration on the diffusion of sodium ions through the aluminum-doped zeolite BEA system (Si/Al = 30), the grand canonical Monte Carlo method was used to predict the water absorption into aluminosilicate zeolite structure under various conditions of vapor pressure and temperature, followed by molecular dynamics simulations of how the Na diffusion depended upon the concentration of water molecules. The predicted absorption isotherm exhibited the first-order like transition which was commonly observed in hydrophobic porous systems. The molecular dynamics trajectories indicated that the sodium ions diffused through zeolite porous structures via a hopping mechanism. The results showed that, at above 15wt% hydration (good solvation regime), the formation of the solvation cage markedly increased Na diffusion by reducing the hopping energy barrier by 25%; from the 3.8kcal/mol observed in the poor solvation regime.

Sodium Diffusion through Aluminum-Doped Zeolite BEA System: Effect of Water Solvation. H.Kim, W.Q.Deng, W.A.Goddard, S.S.Jang, M.E.Davis, Y.Yan: Journal of Physical Chemistry C, 2009, 113[3], 819-26