Single-crystalline hierarchically-porous TS-1 zeolite catalysts via a solid-phase transformation mechanism

Abstract Hierarchically porous zeolites are a type of very hot catalyst with improved catalytic performances as compared with conventional microporous-only zeolites due to the improved mass transportation among the hierarchical meso/macropores, which are expected to be the next-generation catalysts for conversion of bulky molecules and/or polymers. Moreover, hierarchical zeolites with the single crystalline structure that is an identical registry of micropores within the entire particle identified the less pore blockage and less diffusion limitation compared to an aggregated structure of nano-zeolites. The developed synthetic methods were mostly conducted in a liquid-phase system and usually required expensive additives, such as silanes or mesoporogons, etc. Finding facile and cost-effective synthetic methods have been still challenging. Here, a facile and cost-effective strategy by controlling the growth/crystallization in a solidified hydrogel system was reported for the synthesis of Ti-containing MFI-type zeolites (TS-1) to simultaneously achieve hierarchical porosity, single-crystalline structure, and high catalytic performance in alkene oxidations. The synthesized zeolites were characterized by XRD, SEM, TEM, Nitrogen adsorption analysis, DRUV spectroscopy, IR spectroscopy, etc. The growth processes were also tracked and well-characterized. It was found that the solid-phase transformation mechanism was dominated for forming the hierarchical structure. This strategy could directly produce TS-1 with abundant intracrystalline continuous mesopores and large amounts of active framework titanium species, contributing to higher activity for epoxidation of alkenes compared to the traditional microporous-only TS-1 zeolites.