Chemical Imaging of Hierarchical Porosity Formation within a Zeolite Crystal Visualized by Small‐Angle X‐Ray Scattering and In‐Situ Fluorescence Microscopy

Abstract

Introducing hierarchical porosity to zeolites is vital for providing molecular access to microporous domains. Yet, the dynamics of meso-and macropore formation has remained elusive and pore space ill-characterized by a lack of (in situ) microscopic tools sensitive to nanoporosity. Here, we probe hierarchical porosity formation within a zeolite ZSM-5 crystal in real-time by in situ fluorescence microscopy during desilication. In addition, we introduce small-angle X-ray scattering microscopy as novel characterization tool to map intracrystal meso-and macropore properties. It is shown that hierarchical porosity formation initiates at the crystal surface and propagates to the crystal core via a pore front with decreasing rate. Also, hierarchical porosity only establishes in specific (segments of) subunits which constitute ZSM-5. Such spacedependent meso-and macroporosity implies local discrepancies in diffusion, performance and deactivation behaviors even within a zeolite crystal.Zeolite catalysts are microporous crystalline aluminosilicates, displaying unique shape selectivity through their steric pore space. [1,2] However, such selectivity requires molecu-