Effect of lattice shrinking on the migration of water within zeolite LTA

Abstract

Water adsorption within zeolites of the Linde Type A (LTA) structure plays an important role in processes of water removal from solvents. For this purpose, knowing in which adsorption sites water is preferably found is of interest. In this paper, the distribution of water within LTA is investigated in several aluminum-substituted frameworks ranging from a Si:Al ratio of 1 (maximum substitution, framework is hydrophilic) to a Si:Al ratio of 191 (almost pure siliceous framework, it is hydrophobic). The counterion is sodium. In the hydrophobic framework, water enters the large {\alpha}-cages, whereas in the most hydrophilic frameworks, water enters preferably the small $\beta$-cages. For frameworks with moderate aluminum substitution, $\beta$-cages are populated first, but at intermediate pressures water favors $\alpha$-cages instead. Framework composition and pressure therefore drive water molecules selectively towards $\alpha$- or $\beta$-cages.