Soft-templating synthesis of hierarchical mordenite as high-performance catalyst for cyclic acetals production via acetylation of glycerol and benzaldehyde.

Highly active hierarchical mordenite zeolite with micro/mesoporosity (TM- n) for selective synthesis of cyclic acetals via acetylation reaction is reported. The hierarchical zeolite is synthesized using soft-templating approach with variations in octadecyltrimethoxysilane (OTMS/Al 2 O 3 ratio, n = 0.2, 0.3 and 0.4) in precursor hydrogels. The results reveal that OTMS not only creates secondary mesoporosity in zeolite framework (larger mesopore volume, external surface area, average pore diameter), but also influences the crystallization process, altering the crystal morphology, crystallinity and Si/Al ratios. Among TM- n zeolites prepared, TM-0.3 hierarchical mordenite has the optimum OTMS amount incorporated while further increasing the OTMS amount leads to the formation of ANA/GIS intergrowth. Thanks to the accessible hierarchical porosity, reduced acidity and morphological effects, the TM-0.3 hierarchical mordenite exhibits excellent catalytic performance (84.1% conversion, TOF = 0.087 s−1, 61.5% dioxolane selectivity) in acetylation of glycerol and benzaldehyde (160 °C, 20 min) better than pristine mordenite. The catalyst is reusable for five runs with minimal loss of activity (TOF = 0.087 → 0.084 s−1), making it a promising catalyst for chemical productions involving bulky molecules. In addition, comparative catalytic tests with classical homogeneous and heterogeneous catalysts, including H 2 SO 4 , HCl, CH 3 COOH, H–Y, H-LTL, Na-X, Na-A, were performed. [Display omitted] • Hierarchical mordenite is crystallized using new organosilane via soft templating method. • Octadecyltrimethoxysilane (OTMS) serves as a mesoporogen. • OTMS governs crystallization process, affecting morphology, crystallinity and Si/Al ratio. • Hierarchical modernite catalyst is very active in acetalization of benzaldehyde and glycerol. • 84.1% conversion with 61.5% selective to dioxolane is recorded at 160 °C for 20 min. [ABSTRACT FROM AUTHOR]