Fast synthesis of hierarchical Al-free Ti-BEA plate-like nanocrystals from low-templated dry gel via a steam-assisted conversion method

摘要

A hierarchical nanosized Ti-BEA zeolite was prepared via a green steam-assisted conversion (SAC) method taking inorganic titanium source as the raw material. Neither aluminum source nor hydrofluoric acid was required, instead, only a bit of template agent (TEAOH/SiO2 = 0.2) and 2 days period were sufficient, much less than that reported (TEAOH/SiO2 >= 0.55, 7-14 days). Comprehensively, the role of seeds, alkali ions, and ion exchange on the physicochemical properties of Ti-BEA products were investigated via a series of characterization. Innovatively, the tetracoordinated Ti active sites could be directly constructed by a simple ion exchange process instead of conventional acid washing; furthermore, the mechanism of ion exchange inducing Ti coordination transformation was also proposed to guide other titanosilicate zeolites. Excellent Ti active sites, surface properties, and textural properties endowed the Ti-BEA catalyst with excellent activity over cyclohexene epoxidation, while its synthesis procedure and cost were far better than reported.