Direct Identification of Zeolite Beta Polymorphs by Solid-State 29Si Nuclear Magnetic Resonance Spectroscopy

Stacking disorder and polymorphism in zeolite and zeolite-like materials hinder their structural characterization. In this work, we propose an advanced approach based on applying pure shift solid-state Si-29 nuclear magnetic resonance (NMR) spectroscopy for the structural investigation of zeolitic materials containing intergrown polymorphs. The approach developed in the case study of zeolite beta allows for the resolution of 21 Si-29 signals, attributing them to non-equivalent T sites in polymorphs A, B, and C, reconstruction of individual Si-29 magic angle spinning NMR spectra for each polymorph, and determination of the polymorph composition with higher accuracy than Xray diffraction. The results reveal that two widely used synthetic routes for zeolite beta, alkaline and fluoride synthesis, lead to different polymorph compositions. These findings indicate that pure shift solid-state Si-29 NMR can serve as a superior tool for the elucidation of polymorphism in zeolites.

Automated summary

In this study, an advanced approach based on pure shift solid-state Si-29 NMR spectroscopy was proposed for the structural investigation of zeolitic materials with polymorphs. The results showed that this approach could accurately determine the polymorph composition and overcome the interference of stacking disorder and polymorphism. The study also discovered the differences in polymorph composition under different synthesis routes.