Circumventing the Direct Textural Characterization of Presumed Hierarchical Zeolites: The Case of Surfactant-Templated USY Zeolites
Résumé
The presence of intracrystalline mesopores in hierarchical zeolites is often difficult to prove with standard and even advanced characterization techniques. Zeolite-templated carbons (ZTCs) develop within the zeolite microporosity and are hence a negative copy of their porous structure. Textural characterization of the ZTCs allows for circumventing the difficulty in assessing the presence of intracrystalline mesoporosity in the presumed hierarchical zeolite. A set of surfactant-templated USY zeolites was prepared using surfactants with increasing chain lengths, and the corresponding ZTCs were synthesized. The textural characterization of the hybrid materials (zeolite/ZTC) and of the ZTCs (after zeolite dissolution) achieved from surfactant-templated zeolites allowed us to conclude the absence of intracrystalline tailored mesoporosity. Zeolites achieved upon surfactant-templating should hence rather be described as composite materials. The difficulty in assessing the composite nature of these surfactant-templated zeolites is due to the formation of the tailored mesoporosity within the larger (steamed) mesoporosity of the parent zeolite.
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