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An exact knowledge of the architecture of complex pore networks and the impact on transport processes is critical to understand and optimize their integration in many functional solids. Here, a robust and versatile approach is demonstrated to quantitatively map pore constrictions within hierarchical faujasite-type (Y and USY) zeolites, the most widely applied zeolitic materials in industry. Differential hysteresis scanning measurements by high-resolution argon sorption coupled with an advanced modeling framework enable the derivation of the amount and size of pyramidal, constricted, and occluded mesopores. This yields unprecedented insight into the impact of widely practiced demetallation treatments on the porosity evolution and clearly highlights the interplay between the geometry of mesopores developed by a given treatment and those introduced by previously applied postsynthetic modifications. Based on the findings, the dynamic assessment by positron annihilation spectroscopy confirms the effectiveness of each mesopore type at enhancing the diffusion of ortho-positronium within the crystal. The quantitative descriptors attained by these complementary techniques can revolutionize the design of porous materials for a wide range of applications. [ABSTRACT FROM AUTHOR]

On page 5621, J. Kenvin, J. Pérez‐Ramírez, and coworkers demonstrate differential hysteresis scanning by high‐resolution argon sorption and positron annihilation spectroscopy as powerful tools to quantify the complex architecture of pore networks in hierarchical faujasite zeolites and their efficiency in transport processes. The descriptors attained by these complementary techniques further advance the design of porous materials for a wide range of applications. The creatures in the cover, exploring a tortious cave system, exemplify the challenges with pore accessibility and connectivity. [ABSTRACT FROM AUTHOR]

Abstract: The improvement of molecular transport properties of hierarchical H-ZSM-5 obtained by desilication was evidenced by studying the desorption of o-xylene and isooctane by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This technique enabled monitoring simultaneously bands associated with the molecular probes and the zeolite, using powdered sample masses as low as 1mg. Two H-ZSM-5 samples with markedly different crystal sizes were investigated. The first sample was commercial and consisted of small crystallites (ca. 250nm). The second sample were laboratory-made large crystals with coffin-like shape (ca. 17×4×4μm3). The hierarchical derivatives of the small and large zeolite crystals displayed 250 and 120m2 g−1 of mesopore surface area, respectively, in contrast to the 62 and 5m2 g−1 of the parent counterparts. The data based on o-xylene desorption were partly disguised by site-desorption limitations. Desorption experiments using isooctane evidenced a 4-fold reduction in the characteristic diffusion path length on both mesoporous small and large zeolites with respect to their purely microporous analogues. These results confirm the substantial potential for improvement of commercial nanocrystalline zeolites in diffusion-limited reactions upon the introduction of intra-crystalline mesoporosity by post-synthesis modification. [Copyright &y& Elsevier]