The grand canonical Monte Carlo method was used to investigate the effect of hydration upon the diffusion of sodium ions (table 11) through aluminum-doped zeolite BEA system (Si/Al = 30), and to predict water absorption into the aluminosilicate structure under various conditions of vapor pressure and temperature. Molecular dynamics simulations were used to investigate how Na diffusion depended upon the concentration of water molecules. The predicted absorption isotherm indicated a first-order like transition; as commonly observed in hydrophobic porous systems. The molecular dynamics trajectories indicated that the Na ions diffused through zeolite porous structures via a hopping mechanism. The results showed that, above 15wt% hydration, the formation of the solvation cage markedly increased Na diffusion by reducing the hopping energy barrier by 25% from the value of 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

Table 10

Diffusion in Various Zeolites

Table 10 (continued)

Diffusion in Various Zeolites