Synthesis and characterization of hierarchical titanium-containing mesoporous materials with MFI crystalline structure using the gas phase recrystallization for the improvement of olefins epoxidation activity

Here we propose the synthesis of hierarchically titanium-containing mesoporous materials with MFI crystalline structure through the effective and fast post recrystallization method. The post recrystallization method consists of two steps. The first step was the easy impregnation of the structure directing agent of MFI crystalline structure on calcined mesoporous materials. The second step was the fast steam assisted conversion (SAC) process. The mother supports (Ti-MCM-41 and Ti-SBA-15) are prepared using the modified hydrothermal synthesis method, and the SAC process is conducted using the fully dried tetrapropylammonium hydroxide impregnated mother supports under an autogenous steam pressure condition in an autoclave. The prepared materials are investigated using various characterization methods. The recrystallized mesoporous materials exhibit the MFI crystalline structure both in the pore as well as on the surface, and the Ti and Si species are rearranged on an atomic level. The mesoporosity is maintained depending on the SAC process time. The influences of the recrystallization are investigated using the olefins epoxidation. The recrystallization induces the increase of more active titanium species and the surface become more hydrophobic. These influences clearly reveal the improvements in the catalytic activity. The recrystallized mesoporous materials exhibit higher catalytic activity. The conversion and selectivity are improved and the side reactions are decreased significantly.