Two-dimensional (2D) zeolite nanosheets open exciting opportunities for the application in catalysis and separations. Exfoliation of layered zeolite shows a promising way for the preparation of 2D zeolite nanosheets. Herein, non-swollen MCM-22P with ordered layer spacing was successfully exfoliated to dispersible MWW nanosheets. Firstly, a wet-oxidization method, i.e., heating in a mixture of H 2 SO 4 and H 2 O 2 (called piranha solution) was adopted to remove the template of pyridine (PI) from as-synthesized MCM-22P zeolite. IR, TG, XRD , N 2 adsorption confirmed that the wet-oxidization could efficiently remove PI from MCM-22P zeolite while preserving the MWW crystal structure. Exfoliation of the detemplated MCM-22P zeolite was successfully achieved by an ultrasonic treatment in water. After purification by sedimentation, 2D MWW zeolite nanosheets dispersed in aqueous solution were obtained. The monolayer MWW nanosheets with high purity are confirmed by SEM and TEM observations. The wet oxidation followed by the sonication method provides an alternative way for the exfoliation of layered zeolite to dispersed nanosheets.
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 HNO 3 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.
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