Modelling the effect of water on cation exchange in zeolite A

Classical energy minimisation techniques have been employed to model the effect of hydration on the adsorption behaviour of extra-framework cations Na+, Cs+, Ca2+, Ba2+, Cd2+ and Sr2+ in zeolite A. The experimental structure of zeolite CaNa-A (Si/Al = 1) is reproduced accurately, while the energetically preferred position for water molecules is calculated to be inside the α-cage, in agreement with experiment. The preferential locations for the sodium and calcium ions in the hydrated zeolite A are governed by the water molecules and are calculated in the siliceous structure to be the β-cages (S6R position) for Na+ and β-cages (S6R′ positions) for Ca2+. These locations are in agreement with experimental findings of zeolite A structures, but have not previously been calculated for the calcium position.