Framework Flexibility Governs Molecular Accessibility and Selectivity in Zeolite Catalysts.

Crystalline microporous zeolites are pivotal materials in the petrochemical industry, catalysis, separation, and energy conversion. Their performance arises from ordered frameworks that govern molecular transport and reactivity, complemented by tunable acidity. Although traditionally regarded as rigid, zeolite frameworks display remarkable structural flexibility under working conditions, a feature often overlooked but crucial for understanding their catalytic activity. Here, we report the direct imaging of nanozeolite flexibility during ethanol conversion using in situ Bragg coherent diffractive imaging (BCDI). We directly visualize and quantitatively measure zeolite flexibility through its interconnected manifestations as lattice distortion and strain. Three-dimensional strain maps reveal dynamic, facet-specific distortions that correlate with the anisotropic channel orientations of the MFI framework, establishing a link among directional flexibility, molecular selectivity, and catalytic performance. Our measurements achieve picometer-level strain sensitivity and picojoule-scale deformation energy quantification, providing unprecedented insight into the energetics of zeolite framework elasticity. These findings challenge the rigid-host paradigm and establish flexibility as a major parameter for tuning molecular accessibility and selectivity. More broadly, they demonstrate how coherent X-ray imaging can capture real-time lattice dynamics in complex materials, paving the way for adaptive catalysts and advanced separation processes that harness the structural flexibility for enhanced performance.