Controlled Crystallization of Hierarchical Monoliths Composed of Nanozeolites

Micro-/macroporous and meso-/macroporous amorphous silica monoliths have been prepared and transformed into ZSM-5 nanosheet zeolitic macroporous monoliths. The hierarchized zeolite monoliths have been optimized in terms of crystallinity rate by varying durations and temperatures of hydrothermal treatments. Fully crystallized ZSM-5 nanosheet monoliths were obtained after a combination of two consecutive hydrothermal treatments at 150 °C for 5 days with stirring and at 120 °C for 1 day under static conditions. A ZSM-5 nanosheet monolith similar in shape and dimensions to the original amorphous micro-/macroporous silica monolith was obtained, but a partial reduction in size was observed for the ZSM-5 nanosheet monolith obtained from the amorphous meso-/macroporous silica monolith due to a partial dissolution. Results showed that the macropores of the parent silica monoliths were preserved after the transformation with similar diameter sizes but with wider pore size distribution and additional mesopores systems thanks to the nanosheets morphology.