Textural characterization of zeolites with complex pore systems: The case of dealuminated mordenite zeolites

Understanding the impact of hierarchization treatments on microporosity and accessibility is crucial for providing comprehensive insights into the interaction of organic molecules with zeolite active sites. A series of dealuminated mordenite zeolite samples was prepared through a sequence of treatments including steaming, acid leaching, and NH4F etching, with increasing severity compared to the parent sample. In this study, we have investigated the influence of these post-synthetic treatments on the micropore size distribution of mordenite using high-resolution argon physisorption isotherms at 87 K. By performing n-nonane preadsorption experiments followed by argon physisorption at 87 K, an unexpected confinement effect attributed to the presence of side pockets was observed. The different dealumination strategies significantly affect both the micropore distribution and the confinement of n-nonane in mordenite zeolite. Steaming treatment exhibited a severe impact on the side pocket fraction, leading to the generation of micropores larger than the main channel cavities. Moderate acid leaching preserved side pockets and impacted main channel fraction. NH4F etching minorly affected the distribution of micropores. An accessibility index (φAr) calculated by comparing argon porosimetry realized before and after n-nonane preadsorption was defined to quantify the micropore enlargement.