Enthalpy of formation and dehydration of lithium and sodium zeolite beta

Zeolite Li-BEA and Na-BEA with Si/Al = 3–4 were synthesized by alumination and ion exchange, then characterized by XRD, TG–DSC and NMR. The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25 °C are 25.6 ± 1.7 kJ/mol TO2 for the dehydrated zeolite and −8.45 ± 0.94 kJ/mol TO2 for the fully hydrated zeolite; for Na-BEA they are −2.4 ± 0.6 kJ/mol TO2 for the dehydrated and −17.8 ± 1.0 kJ/mol TO2 for the fully hydrated zeolite. The integral dehydration enthalpy at 25 °C is 33.2 ± 1.8 kJ/mol H2O for Li-BEA and 16.5 ± 1.1 kJ/mol H2O for Na-BEA. The partial molar dehydration enthalpies of both Li-BEA and Na-BEA are a linear function of water content. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents.