Determination of Polymorph A-Enrichment and Absolute Structure of Chiral Zeolite Beta Through Electron Crystallography.

Abstract

Zeolite Beta, one of the earliest recognized chiral zeolitic systems and widely used in the chemical industry, poses a significant challenge for characterizing its chiral structure because of its intergrowth of polymorphs. Herein, we report a comprehensive electron crystallography framework for the determination of polymorph ratios, absolute structures, and enantiomeric distributions in zeolite Beta. By developing an optimized real-space imaging protocol based on scanning transmission electron microscopy, we circumvent the mechanical tilting limits of electron microscopy, enabling chiral identification even at arbitrary crystal orientations. Furthermore, we introduce a weighted refinement strategy for 3D electron diffraction (3D ED). By utilizing dynamical diffraction simulations to derive weighting factors from enantiomeric intensity disparities, the sensitivity of absolute structure determination is significantly enhanced, overcoming the dilution of chiral signals by centrosymmetric components. Experimental validation confirms that this integrated approach accurately quantifies regional polymorph A enrichment and successfully discriminates between P4₁22 and P4₃22 enantiomers. This work not only addresses long-standing challenges in characterizing intergrown chiral zeolites but also provides a refined methodological paradigm for investigating such complex porous materials.