Studies on inclusion complexes and dyanmic properties of sodium ion in zeolite-A

Abstract

Part A; Molecular inclusion by hydroxy host molecules (9-hydroxy-9-(1-propynyl) fluorene and 1,1-bis (2,4-dimethylphenyl)-2-butyn-1-o1) with hydroxy guest molecules (water and various alcohols) has been investigated by using an empirical potential function. Water, methanol, ethanol, and n-propanol have been employed as guest molecules and their relative stabilities in the complexes are considered. In order to explain the inclusion phenomena the sufficient number of (Host + Guest) units should be considered. As a calculated result, alcohol is found to be more stable than water as a guest molecule in the two tested hydroxy inclusion complexes, which is well agreement with experimental result. It is also found that the nonbonded interaction is the most important factor in determination of the relative stabilities of the hydroxy inclusion complexes. Part B; Molecular dynamics (MD) calculations of Na ions in A-type zeolite framework were carried out with empirical potential energy functions. Two type of zeolite-A model was employed at four different temperatures in MD simulation, one is pseudo cell and the other is true unit cell. The simulated diffusion mechanism shows a good agreement with the experimental one. In the diffusion of Na ion in the zeolite-A, only $Na_{II}$ and $Na_{III}$ ions contribute much to the diffusion and $Na_I$ ion does not diffuse significantly even at high temperature, which is a reasonable diffusion mechanism of sodium ion in zeolite-A with respect to the conductivity experiments. But the simulated diffusion coefficient of Na ion at 400 K is not very good even with the large model. The motion of Na ion is projected to the normal coordinate of each ion as a function of time, and then the vibrational frequency of each vibrational normal mode is obtained, and a good agreement with I.R. spectral value is obtained.