DESIGN OF HIGHLY EFFICIENT LIQUID-PHASE OXIDATION CATALYSTS OF TITANOSILICATES THROUGH PRECISE CONTROL OF ZEOLITE STRCUTURES

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Titanosilicates containing tetrahedral Ti ions in zeolite framework prove to be attractive catalysts owing to their capability of oxidizing a variety of organic compounds with clean oxidant of hydrogen peroxide in the liquid-phase. In the last two decades, the studies have been focused on two representative titanosilicates, MFI type TS-1 and BEA type Ti-Beta. However, these two titanosilicates have a lot of difficult problems to be tackled. Medium-pore TS-a lacks the ability to oxidize bulky substrates, and there is still a large space to improve its specific activity per Ti site. Ti-Beta, on the other hand, encounters serious disadvantages of easy leaching of Ti active species probably due to its structural stacking faults. From the viewpoint of developing new heterogeneous catalytic processes for alkene epoxidation, it is urgent to prepare more efficient titanosilicates. In this study, we have succeeded in incorporating Ti into MWW zeolite of a very unique pore structure, which leads to a new generation of titanosilicate catalyst. Both hydrothermal synthesis using boric acid as a crystallization-supporting agent and postsynthesis through a reversible structural conversion result in Ti-MWW catalysts extremely active for alkene epoxidation. Ti-MWW is also converted into the catalysts with accessible reaction spaces suitable for bulky reactions by delamination or novel acid treatment.Modification methods for developing highly active and selective catalysts from Ti-Beta have also been established. The methods involve selective poisoning of acid sites and fluorine contained within the structure of Beta zeolite, but without negative influence on the catalytic performance of framework Ti species.Ti-containing mesoporous materials, Ti-SBA-15 and Ti-MSU-G which have higher hydrothermal stability and are stable against Ti leaching have been prepared successfully by novel postsynthesis method and direct hydrothermal synthesis, respectively.