Study on the adsorption of water on NanZSM-5 type zeolite:: Molecular simulation

Molecular dynamic (MD) quench method and grand canonical Monte Carlo method (GCMC) are used to study the adsorption of water on Na(n)ZSM-5 type zeolite. The simulated adsorption isotherm is in good agreement with the experimental data reported in literatures. Based on these facts, adsorption of water on Na(n)ZSM-5 with various n(Si)/n(Al), ratios is predicted. The simulation results indicate that n(Si)/n(Al) ratio of zeolite framework affects the water adsorption and adsorption isotherms greatly and the adsorption amount decreases as the n(Si)/n(Al) ratio increases, which can be explained by that the atomic charge of Na' cation would influence greatly the polar water molecules due to the Coulomb force. The adsorbed water molecules are located around Na cations and At atoms on the zeolite framework and the average number around Na cation and Al atom is four at lower loading. However, there are hydrogen bonds between the adsorbed water molecules and the oxygen atoms on the zeolite frameworks at higher loading. At the same loading, the isosteric heat decreases as the n(Si)/n(Al) ratio increases.