Crystallization of as-Mesocellular Silica Foam into Hierarchical TS-1 Zeolites by Conventional Hydrothermal and Dense-Gel Routes for Oxidation Reactions

Crystallization of as-mesocellular silica foam (as-MCF) into TS-1 zeolites by conventional hydrothermal and dense-gel routes is reported. The TS-1 synthesized through the dense-gel route (TS-1- d ) showed higher meso-macroporosity (0.311 vs 0.233 cm 3 /g), smaller particle size (130 vs 305 nm), and enhanced external surface area (86 vs 31 m 2 /g) than that synthesized under conventional hydrothermal conditions (TS-1- h ). These might suggest that an organic template from as-MCF acted as mesoporogen in the dense-gel synthesis; however, segregation of the organic template and the synthesis mixture occurred in the conventional hydrothermal synthesis. The obtained TS-1 from the crystallization of as-MCF showed an enhanced framework Ti. The turnover frequencies (h -1 ) of TS-1- d toward hydroxylation of phenol and oxidation of dibenzothiophene (DBT) were 2 and 5 times, respectively, higher than those by TS-1- h . The DBT conversion by TS-1- d reached >99.0%, while it was only 63% by TS-1- h , suggesting the potential of TS-1- d for deep desulfurization of the fuels. Consequently, the crystallization of as-mesoporous materials through the dense-gel route is a promising approach to prepare TS-1 zeolites with smaller particle sizes and enhanced mesoporosity.