(582bv) Nature and Consequences of Al - Al Interactions in SSZ-13 Zeolite
We calculated the total energies of two protons each associated with an O adjacent to Al, and reported these energies relative to the isolated BrÃ¸nsted site energy. At a given Al separation there is a range of energies corresponding to the proton associated with each of the four symmetry-distinct O atoms.Â At third-nearest-neighbor separation, energies begin toÂ decrease relative to the infinite limit. Energies are minimized at first-nearest-neighbor separation, suggesting that Al sites experience an attractive potential in the acid-form, and in this form the Al will tend to aggregate. As laboratory-prepared zeolites generally follow LÃ¶wensteinâs rule, the DFT results show that this rule is not a consequence of the underlying energy landscape experienced by the Al sites. Further, at conditions at which Al become mobile on the SSZ-13 lattice, e.g. high temperature steaming, the Al experience an attractive interaction that may lead to Al aggregation and ultimately provide a route to dealumination. The results provide a baseline for considering the influence of other extra-lattice ions.
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