Santikary, Prakriteswar ; Yashonath, Subramanian (1994) Dynamics of zeolite cage and its effect on the diffusion properties of sorbate: persistence of diffusion anomaly in NaA zeolite Journal of Physical Chemistry, 98 (37). pp. 9252-9259. ISSN 0022-3654
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Official URL: http://pubs.acs.org/doi/abs/10.1021/j100088a027
Related URL: http://dx.doi.org/10.1021/j100088a027
Abstract
Recent computer simulations on zeolites Y and A have found that the diffusion coefficient and the rate of intercage diffusion exhibit, apart from a linear dependence on the reciprocal of the square of the sorbate diameter, an anomalous peak as sorbate diameter approaches the window diameter. Here we report molecular dynamics simulations of zeolite NaA incorporating framework flexibility as a function of sorbate diameter in order to verify the existence of anomalous diffusion. Results suggest persistence of anomalous diffusion or ring effect. This suggests that the anomalous behavior is a general effect characteristic of zeolites Y and A. The barrier for diffusion across the eight-ring window is seen to be negative and is found to decrease with sorbate size. The effect of sorbate on the cage motion has also been investigated. Results suggest that the window expands during intercage migration only if the sorbate size is comparable to the window diameter. Flexible cage simulations yield a higher value for the diffusion coefficient and also the rate of intercage diffusion. This increase has been shown to be due to an increase in the intercage diffusions via the centralized diffusion mode rather than the surface-mediated mode. It is shown that this increase arises from an increase in the single particle density distribution in the region near the cage center.
Item Type: | Article |
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Source: | Copyright of this article belongs to American Chemical Society. |
ID Code: | 55833 |
Deposited On: | 19 Aug 2011 05:41 |
Last Modified: | 19 Aug 2011 05:41 |
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