Abstract
Abstract This work studies the thermal stability, heat-induced structural deformations, and dehydration/rehydration dynamics of a synthetic high silica mordenite. It is of special interest because this particular phase has proven to be an ideal host for the encapsulation of several kinds of organic molecules making it a promising scaffold for drug delivery. The dehydration process was followed by thermal analysis, infrared spectroscopy in controlled atmosphere, in situ synchrotron XRPD, and structural refinement. Overall, all the results indicate weak interactions of H2O molecules with the silicatic mordenite framework and evidence the presence of hydroxyl groups with different condensation responses at high temperature. Infrared characterization highlighted how the desorption of adsorbed H2O molecules under degassing is already complete at rT. The unit cell parameters exhibit very slow and almost isotropic changes upon heating. Above 550 °C an increase in slope is observed for all parameters. This corresponds to the marked silanol condensation and consequent framework reassessment observed at this temperature by infrared characterization. Overall cell contractions are 0.67%, 1.18%, and 0.81% for a, b, c, respectively and 2.64% for cell volume. HS-MOR undergoes very moderate T induced deformations, indicating a very rigid and stable framework.
Highlights
The shape selective properties of zeolites are at the basis of their success in adsorption processes and catalytic activity
In this paper we report the intrusion of an azeotrope solution in an all silica chabazite (Si-CHA) under pressure
The results of this work show that, when Si-CHA is immersed in the ethanol/water azeotrope solution, it immediately absorbs both H2O and ethanol molecules, even at ambient conditions
Summary
The shape selective properties of zeolites are at the basis of their success in adsorption processes and catalytic activity. One of the challenges in renewable energy fuel production is the purification of ethanol from water. While the water/ethanol separation in ethanol rich solutions by hydrophilic zeolites is extremely effective (e.g. LTA membranes [5]), the ethanol/water separation performances in H2O rich solutions operated by hydrophobic zeolites are definitely worse. This is due to the presence of silanol defects, or Al hydrophilic sites - accidentally present in “nominally silicatic“ zeolites which favor the adsorption of water molecules during the purification process
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