Thermal behavior of high silica mordenite

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.