Enthalpy of formation and dehydration of alkaline earth cation exchanged zeolite beta

Abstract

Cationic variants of zeolite beta (Mg-BEA 14, Ca-BEA 14, Sr-BEA 14, Ba-BEA 14, Mg-BEA 4 and Ca-BEA 4) were achieved by alumination and ion exchange processes, and characterized by XRD, NMR and TG–DSC. Mg-BEA 14/Ca-BEA 14, Sr-BEA 14/Ba-BEA 14, and Mg-BEA 4/Ca-BEA 4 have distinct thermal behavior. The low silica zeolites Mg-BEA 4 and Ca-BEA 4 were observed to have octahedral Al atoms and less crystallinity compared with high silica Mg-BEA 14 and Ca-BEA 14. High temperature oxide melt solution calorimetry determined the dehydration enthalpy and the formation enthalpy from the constituent oxides. For alkaline earth zeolite beta with the same Si/Al ratio, both the integral dehydration enthalpy and formation enthalpy from oxides becomes more endothermic with increasing average ionic potential. Mg-BEA 4 and Ca-BEA 4 have very endothermic formation enthalpies, in both dehydrated and hydrated forms, indicating a likely thermodynamic barrier to their direct synthesis, despite the natural occurrence of their analog, tschernichite.