Acid-modulated synthesis of ultra-thin Ti-MWW zeolite nanosheets for the efficient epoxidation of cycloalkenes with tert-butyl hydroperoxide

Abstract

The Ti-MWW zeolites with a layered morphology, synthesized by a conventional method, usually show low catalytic activities in the epoxidation of bulky alkenes due to the serious steric constraint imposed by the zeolite micropores and the adverse effects from some extra-framework octahedral Ti species. In the present work, the Ti-MWW zeolite was prepared by the reaction of an ultra-thin layered borosilicate MWW-type zeolite (D-ERB-1) with tetrabutyl orthotitanate (TBOT) in a HNO3 aqueous solution, wherein D-ERB-1 was hydrothermally synthesized by introducing an organosilane into the synthetic gel. In combination with the results from extensive characterizations for the synthesized zeolites, it is found that the currently synthesized Ti-MWW zeolite without extra-framework octahedral Ti species has thinner nanosheets that are very helpful to the epoxidation of cycloalkenes with tert-butyl hydroperoxide (TBHP), and is more active than the conventional Ti-MWW and other titanosilicate zeolites. Moreover, the developed catalyst is recyclable after the regeneration of the deactivated zeolite by washing with acetonitrile (MeCN). Therefore, the present work provides some guidance in the development of an efficient titanosilicate catalyst for the epoxidation of bulky alkenes.