Quantifying the Complex Pore Architecture of Hierarchical Faujasite Zeolites and the Impact on Diffusion

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.