Postsynthesis of extremely active Ti-MWW through a structural conversion method

摘要

B-free titanosilicate with the MWW structure, Ti-MWW, has been postsynthesized from highly deboronated MWW silicalite using a novel method in which a reversible change of three dimensional MWW structure into its lamellar precursor and Ti incorporation occurred simultaneously. This method allowed a homogeneous Ti incorporation through the framework sites. Ti-MWW thus prepared proved to be more active and selective than hydrothermal synthesized one in the epoxidation of cyclohexene, 1-hexene and allyl alcohol with hydrogen peroxide. When used Ti-MWW was regenerated by calcination, high conversion and product selectivity were totally maintained, and no obvious Ti leaching was observed, which indicated that the Ti species incorporated by the present method were highly stable. The higher specific activity of post-incorporated Ti was partially due to the removal of the framework boron, and more importantly was attributable to the occurrence of new type Ti species.