Study on Adsorption of Water on NanZSM-5 Type Zeolite by Molecular Simulation

Molecular dynamic (MD) quench method and grand canonical Monte Carlo method (GCMC) are used to study the adsorption of water on NanZSM-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 NanZSM-5 with various nSi/nAl ratios is predicted. The simulation results indicated that nSi/nAl ratios of zeolite framework affect the water adsorption and adsorption isotherm greatly and the adsorption amount decreases with the increase in the nSi/nAl ratio. The above observation can be explained by assumption of the charge influence of Na+ cations on the polar water molecules due to the Coulomb force. The adsorbed water molecules are located around Na+ cations and Al atoms on the zeolite framework and the average number around Na+ cations and Al atoms is four at lower loading. However, hydrogen bonds between the adsorbed water molecules and the oxygen atoms on the zeolite framework exist at higher loading. At the same loading, the isosteric heat decreases as the nSi/nAl ratio increases.