Structure of an aluminophosphate EMM-8: a multi-technique approach

Area of Science:

• Materials Science
• Crystallography
• Solid-State Chemistry

Background:

• Aluminophosphate molecular sieves are crucial in catalysis and separation.
• Understanding the precise framework structure of novel materials like EMM-8 is essential for optimizing their properties.
• Previous studies on related materials highlight the importance of structural characterization.

Purpose of the Study:

• To determine the crystal structure of the aluminophosphate EMM-8 in its calcined, anhydrous form.
• To investigate the local environments of phosphorus and aluminum atoms using solid-state NMR.
• To elucidate the structural changes upon calcination and hydration.

Main Methods:

• Synchrotron powder diffraction data analysis using the FOCUS program.
• Rietveld refinement for structural model fitting.
• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy to probe local atomic environments.

Main Results:

• The crystal structure of EMM-8 was successfully determined, featuring a framework of double four-ring (D4R) units with 12- and 8-membered ring channels.
• Solid-state NMR detected significant differences between as-synthesized and calcined EMM-8, indicating changes in local symmetry of P and Al atoms.
• The NMR data provided critical constraints for the structural determination from powder diffraction, confirming structural preservation after calcination compared to SSZ-51.

Conclusions:

• The crystal structure of EMM-8 was elucidated, revealing a unique framework topology.
• Solid-state NMR is a powerful tool for understanding local structural changes and guiding crystal structure determination of microporous materials.
• The structural integrity of EMM-8 is maintained after calcination, suggesting its potential for high-temperature applications.