Facile synthesis of hydrothermally stable mesoporous ZSM-5 zeolite from Al- SBA-16 via steam assisted crystallization

In this work, Al grafted SBA-16 (Al-SBA-16) is converted into a fully crystalline hierarchical mesoporous ZSM-5 zeolite with hydrothermal stability by steam assisted crystallization under controlled conditions. The secondary mesoporosity is due to reorganization and recrystallization events happening upon steaming the precursor. Two mesoporous aluminosilicates (Al-SBA-16s) are used as the precursors of zeolites. The precursors are obtained by post-synthetic Al grafting on the silica walls of SBA-16 with aluminium isopropoxide and sodium aluminate. Mesoporous ZSM-5 zeolites obtained from the Al-SBA-16 precursors and commercial ZSM-5 are characterized using XRD, XRF, FT-IR, TEM, N2 adsorption, 27Al and 29Si MAS NMR, and TPD of NH3. The results indicated the presence of intraparticle mesoporosity in the prepared mesoporous zeolites and they have comparable crystallinity with commercial ZSM-5. Catalytic activity of the synthesized mesoporous zeolites in benzylation of mesitylene is found to be comparatively more than commercial ZSM-5, which shows existence of micro/meso hierarchical structure in the mesoporous ZSM-5 zeolites. The aluminium sources, aluminium isopropoxide and sodium aluminate have a remarkable influence on the textural, acidity, and hydrothermal stability characteristics of the synthesized mesoporous ZSM-5 zeolites.