Self-diffusion of water into a ferrierite-type zeolite by molecular dynamics simulations

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Abstract
Previous work in our laboratory described the application of molecular dynamics (MD) to the study of water within such complex models as zeolite systems. In particular, the description of well suited interaction potentials, taking into account periodicity and long-range effects, was of relevance. In this contribution, the application of MD to the study of water inside ferrierite is extended to several systems distinguished by different water coverages. It is shown that the self-diffusion character increases for higher water coverage owing to randomization of the translational movements inside the large pores where the interactions with the framework are not too important. An increase in the self-diffusion coefficient is also observed inside small pores when the modelled Brønsted-acid groups are no longer accessible. Comparisons with available experimental neutron diffusion spectra for various hydrated zeolites show that MD is convenient for simulating the translational movements of water molecules within a porous medium, as well as their librational character.