Acidity and Local Confinement Effect in Mordenite Probed by Solid-State NMR Spectroscopy.

Area of Science:

• Catalysis
• Materials Science
• Spectroscopy

Background:

• H-mordenite (H-MOR) zeolites are crucial catalysts with complex pore structures.
• Understanding acidity and host-guest interactions is key to optimizing zeolite performance.
• Acetonitrile serves as a valuable probe molecule for studying zeolite properties.

Purpose of the Study:

• To comprehensively investigate the acidity and host-guest interactions in H-MOR zeolites.
• To elucidate the locations and configurations of Brønsted acid sites (BASs).
• To characterize the confinement effect of H-MOR's dual pores on guest molecules.

Main Methods:

• Solid-state NMR spectroscopy (multinuclear, multidimensional) using acetonitrile (CD3CN) and trimethylphosphine (TMP).
• Adsorption and coadsorption experiments to probe interactions.
• Density Functional Theory (DFT) calculations.
• Quantitative determination of host-guest interactions.

Main Results:

• Identified locations and local configurations of BASs in H-MOR.
• Characterized host-guest interactions and confinement effects in dual pores.
• Revealed two types of acetonitrile mobility in 12-membered ring (12MR) channels: partially restricted and highly flexible.
• Observed temperature-dependent exchange between acetonitrile species.
• Demonstrated highly restricted acetonitrile mobility in 8-membered ring (8MR) channels due to framework confinement.

Conclusions:

• Acetonitrile probe molecule effectively reveals distinct host-guest interactions and mobility within H-MOR's dual pore system.
• NMR and DFT collectively elucidate the influence of pore structure and acid sites on molecular dynamics.
• Findings provide fundamental insights into zeolite-based catalysis and guest molecule behavior.