Energetic Performances of Channel and Cage-Type Zeosils

Abstract

Energetic performances of nine channel or cage-type zeosils (AFI, FER, MFI, MEL, TON, MTW, DDR, STT, and CHA-type pure silica zeolites) are obtained using water intrusion–extrusion isotherms. The water intrusion is obtained by applying a high hydraulic pressure corresponding to the intrusion step. When the pressure is released, these nine “zeosil–water” systems behave like a molecular spring, water being spontaneously expelled out of the cavities of the zeosils (extrusion step). The first part of this study details the energetic characteristics of MEL-type zeosil (Silicalite-2), which displays a molecular spring behavior reproducible over several water intrusion–extrusion cycles. However, solid-state NMR spectroscopy revealed the presence of structure defects (>5%), which are responsible for the low value of the stored energy (6.5 J/g of zeosil). In a second part, the energetic properties of the nine channel or cage-type zeosils are compared. For these samples, structural modifications can be observed by solid-state NMR spectroscopy. An overall view of the characteristics derived from the water intrusion–extrusion isotherms of these nine zeosils is discussed. The relation between the structure type, in particular, the porous system (cages or channels) and the intrusion pressure, is studied to better understand the mechanism of water intrusion and to predict the zeolite behavior (intrusion pressure values) for a given structure type. The Laplace–Washburn relationship seems to be not appropriate for microporous materials. A correlation was found between the intrusion pressure and the pore diameter for channel systems and the largest cage size for cage systems.