MWW-TYPE TITANOSILICATE: NOVEL PREPARATION AND HIGH EFFICIENCY IN THE EPOXIDATION OF VARIOUS ALKENES

摘要

A novel postsynthesis method has been proposed to prepare a highly efficient titanosilicate catalyst with the MWW topology, Ti-MWW. The so-called reversible structural conversion method is based on a structural interchange between 3-dimensional MWW silicate and its lamellar precursor together a simultaneous incorporation of titanium through the treatment with an aqueous solution of titanium source and cyclic amine. This method overcomes the restriction problem between pore windows and titanium precursor probably encountered in the usual method using TiCl_4 vapour at elevated temperatures. The catalytic properties of postynthesized Ti-MWW have been investigated by comparing with hydrothermally synthesized one as well as the conventional titanosilicates of TS-1 and Ti-Beta in the epoxidation of various alkenes with hydrogen peroxide. Ti-MWW proves to be more effective in the epoxidation of both simple and functionalized alkenens. Particularly, the novel postsynthesis method of a reversible structural conversion incorporates more active Ti species into the framework than the conventional hydrothermal synthesis, leading to the most active epoxidation titanosilicate catalyst so far. Ti-MWW has been further delaminated into thin sheet material which possesses an extremely open and accessible surface area but maintains the basic structure of zeolite. Delaminated Ti-MWW catalyzes the epoxidation of bulky substrates of various cycloalkenes more actively than other titanosilicates including mesoporous Ti-MCM-41.