Postsynthesis and Effective Baeyer-Villiger Oxidation Properties of Hierarchical FAU-type Stannosilicate

Sn-Y zeolite, with hierarchical pore systems and extremely low Al content, was successfully prepared via a convenient postsynthetic route which involves proper predealumination and subsequent (NH₄)₂SnCl₆ treatment under mild aqueous condition. The Sn ions were incorporated into the framework of properly dealuminated Y zeolite through reacting with the defect sites generated in the industrial steaming treatment, the first-step acid treatment, and the second Sn incorporation process under acidic conditions. The acidic medium achieved by adding HCl in the Sn incorporation process affected not only the amount of incorporated Sn and residual Al but also the coordination state of inserted Sn ions. Compared with hydrothermally synthesized Sn-Beta, postsynthesized Sn-Y zeolite exhibited outstanding catalytic performances in the Baeyer-Villiger oxidation reactions of ketones especially when bulky tert-butyl hydroperoxide was employed as the oxidant due to an open pore structure of 3-dimensional 12-membered ring (12-MR) channels of FAU topology as well as the dealumination-derived intracrystal mesoporosity. Moreover, alkali metal ions modification was shown to be an effective approach for enhancing the selectivity of lactones.