Energetic Performances of STT-Type Zeosil: Influence of the Nature of the Mineralizing Agent Used for the Synthesis

Abstract

Water intrusion–extrusion experiments were performed at room temperature on pure silica STT-type zeolites (SSZ-23 zeosils). The samples were obtained using two synthesis routes: hydroxide (SSZ-23(OH)) and fluoride media(SSZ-23(F)). 29Si solid-state NMR spectroscopy confirmed the presence of a small amount of silanol defects in the calcined materials which is more pronounced for the SSZ-23(OH) sample. Nevertheless, the amount of silanol defects observed is quite low (<3% for SSZ- 23(F) and <6% for SSZ-23(OH)). After intrusion–extrusion of water, due to the breaking of some siloxane bonds, the number of defect sites increases and consequently part of water still remains in the structure. However, for both SSZ-23 samples, the “STT zeosil–water” system displays a spring behavior and can restore more than 80% of the stored energy corresponding to about 7.0 J·g–1.