Characterization of hierarchical zeolites: Combining adsorption/intrusion, electron microscopy, diffraction and spectroscopic techniques

Conventional and hierarchical faujasite zeolites, which are relevant to xylene separation by adsorption processes, are characterized using a broad set of complementary experimental techniques. In addition to a conventional faujasite zeolite, hierarchical faujasite zeolites consisting either of nanoparticle aggregates or of a layer-like zeolite are considered. For all samples, both the sodium and barium forms of these X zeolites are investigated. With the goal to predict and rationalize the efficiency of these materials for a given application, the fine characterization reported here aims at identifying key parameters such as their multiscale pore size distribution, pore connectivity/morphology, and external surface physical chemistry. X-ray diffraction is first used to probe the different crystalline phases and domain sizes coexisting in each sample. Electron microscopy at different scales (scanning and transmission microscopies) is also used to determine the morphology of the different porosity domains as well as to investigate the core-shell structure of the samples. N2 adsorption and mercury intrusion are then combined to provide a consolidated multiscale pore size distribution of each sample. Furthermore, adsorption scanning curves are determined to analyze the topology/connectivity of the porosity domains. Finally, infrared spectroscopy and nuclear magnetic resonance are used to assess the chemistry of the samples with special focus on their external surface. The combination of these different techniques is found to provide a rich and detailed picture of these heterogeneous and multiscale solids that goes beyond standard routine characterization.