Stepwise dehydration of Cd-exchanged levyne: thermal stability and structural modifications

Area of Science:

• Materials Science
• Mineralogy
• Crystallography

Background:

• Zeolites possess tunable properties via cation exchange.
• Understanding thermal response of modified zeolites is crucial for applications.
• Natural levyne's structural and thermal behavior can be altered by cation content.

Purpose of the Study:

• To investigate the dehydration mechanism of natural levyne exchanged with Cd2+.
• To determine the impact of Cd2+ exchange on levyne's structural modifications and thermal stability.
• To compare the dehydration behavior of Cd-exchanged levyne with that of Ca-exchanged levyne.

Main Methods:

• In situ single crystal X-ray diffraction was employed.
• Natural levyne was exchanged with Cd2+ ions.
• Structural changes were monitored during heating from 50 to 400 °C.

Main Results:

• Dehydration of Cd-exchanged levyne showed initial similarity to levyne-Ca, with cation migration and slight volume contraction.
• A significant unit-cell volume drop (-7%) occurred between 200-250 °C, corresponding to levyne B topology with 50% T-O-T bond rupture.
• Structural collapse initiated at 400 °C, resulting in an 8% smaller unit-cell volume, and the structure became non-rehydratable.

Conclusions:

• Cd2+ exchange significantly enhances the framework disruption in natural levyne upon dehydration compared to Ca2+ exchange.
• The dehydrated Cd-levyne structure (levyne B topology) is stable up to 350 °C but collapses irreversibly at 400 °C.
• The study highlights the critical role of extraframework cations in controlling zeolite structural response to thermal stimuli.