Robust Baeyer-Villiger oxidation over highly mesoporous single-crystalline Sn-Beta zeolite

Catalytic conversions of cyclic ketones into lactones by the Baeyer–Villiger oxidation are particularly attractive for practical applications because catalytic transformations minimize reactant use as well as waste production while simplify processing conditions. Understanding the unique behaviors of highly mesoporous Sn-Beta zeolite catalyst during Baeyer–Villiger oxidation is a challenging research topic. Herein, highly mesopore single-crystalline Sn-Beta zeolite (Sn-Beta-2s) is hydrothermally synthesized via our developed two-step interzeolite transformation strategy. The synthesis mechanism obeys dissolution–recrystallization process, where the degradation step is essential to prepare Sn-Beta-2s zeolite with abundant mesoporous and relatively high hydrophobicity. This single-crystalline Sn-Beta zeolite is adopted to the Baeyer-Villiger oxidation of cyclic ketones as heterogeneous Lewis acid catalyst. Structure-performance relationship reveals that the diffusion performance dominates the product selectivity over three Sn-Beta zeolites. Through the investigation of catalytic mechanism by in-situ FT-IR spectra and DFT calculations, it is found that carbonyl group is activated by zeolitic framework Sn. As for the bulky tert-butyl hydroperoxide oxidant, the reaction can be only triggered on the zeolite surface due to the severe steric constraints within zeolite channels, accounting for the excellent catalytic activity of Sn-Beta-2s zeolite with nanocrystalline nature.