Repulsive Lateral Interaction of Water Molecules at the Initial Stages of Adsorption in Microporous AlPO-11 According to Al NMR and DFT.

Lateral (adsorbate-adsorbate) interactions between adsorbed molecules affect various physical and chemical properties of microporous adsorbents and catalysts, influencing their functional properties. In this work, we studied the hydration of microporous AlPO-11 aluminophosphate, which has an unusually ordered structure upon adsorption of water vapor, and according to Al NMR data, only tetrahedrally or octahedrally coordinated Al sites are present in the AlPO-11. These Al NMR data are consistent with the results of density functional theory (DFT) calculations of hydrated AlPO-11, which revealed the presence of a strong repulsive lateral interaction at the initial stage of adsorption, suppressing the adsorption of water on neighboring (separated by one -O-P-O- bridge) Al crystallographic sites. As a result, of all the different aluminum sites, only half of the Al1 sites adsorb two water molecules and acquire octahedral coordination.