Repulsive Lateral Interaction of Water Molecules at the Initial Stages of Adsorption in Microporous AlPO₄‑11 According to ²⁷Al 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 AlPO₄-11 aluminophosphate, which has an unusually ordered structure upon adsorption of water vapor, and according to ²⁷Al NMR data, only tetrahedrally or octahedrally coordinated Al sites are present in the AlPO₄-11. These ²⁷Al NMR data are consistent with the results of density functional theory (DFT) calculations of hydrated AlPO₄-11, 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.