Abstract
Abstract A novel titanosilicate with the MWW topology, Ti-MWW, has been prepared by direct hydrothermal synthesis using boric acid as a structure-supporting agent, and also by post-incorporation of tetrahedral Ti species into MWW silicalite through controlled structural conversions between 3-dimensional crystalline MWW silicalite and its lamellar precursor. The catalytic properties of Ti-MWW have been compared with those of conventional titanosilicates. Hydrothermally synthesized Ti-MWW proves to be more effective in the epoxidation of linear alkenes including functionalized ones, and also exhibits considerable activity for cycloalkenes using hydrogen peroxide as oxidant. Postsynthesized Ti-MWW, almost free of boron, catalyzes the alkene epoxidation more effectively as a result of the tetrahedral Ti species different from those resulting from the direct synthesis, which turns out to be the most active titanosilicate catalyst for epoxidation so far. The activity of Ti-MWW in the ammoximation of cyclohexanone is superior to that of TS-1, which is being industrially used. A new interlayer-expanded structure analogous to MWW has been prepared in the form of titanosilicate and denoted by Ti-YNU-1. Ti-MWW is further converted by phase delamination into a thin sheet material. Ti-YNU-1 and delaminated Ti-MWW catalyze the epoxidation of bulky cycloalkenes more actively than Ti-MWW or large pore titanosilicates as well as mesoporous Ti-MCM-41.
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