Demontis, Pierfranco and Gulín-González, Jorge and Suffritti, Giuseppe Baldovino and Tilocca, Antonio (2001) Computer simulations of ethane sorbed in an aluminophosphate molecular sieve. Studies in Surface Science and Catalysis, Vol. 140 , p. 221-227. ISSN 0167-2991. Article.
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Classical Molecular Dynamics (MD) simulations have been carried out to study the dynamic properties of ethane sorbed in an AlPO4-5 aluminophosphate. The main purpose is to gain new insight into the diffusive regime controlling the motion of ethane in such one-dimensional microporous structure. In recent experimental studies a standard MSD vs. t linear dependence (normal diffusion) was found, while earlier experiments seemed to reveal a single-file regime for this system. The present calculations show that ethane diffusion follows the standard regime on the time scale of MD simulations: particle passing (leading to normal unidirectional diffusion) is rather frequent over observation times of several nanoseconds. Consequently a single file regime for this system could only be achieved through the formation of stable clusters of ethane molecules that, once formed, move as single larger species in a single file regime. This possiblity has been tested by calculating the lifetimes of ethane clusters of different size: the large lifetimes observed are less than 1 ns, and are further reduced when the flexibility of the host lattice is incorporated in the model. Therefore these simulation support the experimental observation that normal diffusion dominates the motion of ethane in the AlPO4-5.
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