Formation and dehydration enthalpy of ion exchanged zeolite beta

Cationic variants of zeolite beta (Li-BEA, Na-BEA, K-BEA, Rb-BEA and Cs-BEA) were prepared via aqueous ion exchange. High-temperature oxide melt solution calorimetry determined the dehydration enthalpy and the formation enthalpy from the constituent oxides. For the alkali cation exchanged zeolites, the total enthalpy of dehydration per mole of zeolite TO₂ (T = Si, Al) decreases in magnitude in the order Li-BEA ≈ Na-BEA > K-BEA ≈ Cs-BEA > Rb-BEA. This is in the order of decreasing average ionic potential. The dehydration enthalpy per mole of water decreases in the order Li-BEA > Na-BEA > Cs-BEA > K-BEA > Rb-BEA. The enthalpies of formation become more exothermic with decreasing average ionic potential, as has been observed in several other zeolites. Materials Studio software (Accelrys Inc.) was used to investigate location of the alkali cations and bonding of water molecules in BEA zeolites. The somewhat smaller dehydration enthalpy of K-BEA can be attributed to weaker cation-water interaction, weaker cation-framework interaction, and absence of framework-water interaction.