Nanoporous Zeolite\nUTL Decorated with Sn to Catalyze\nthe Baeyer–Villiger Reaction

Stannosilicates with hierarchical pores are greatly desirable\nfor\nthe liquid-phase conversion of ketones into esters or lactones, in\nparticular, requiring open porous spaces. The nanoporous zeolite UTL\nwith a framework Sn(IV) species was constructed successfully using\na fluorine-assisted hydrothermal synthesis strategy. The obtained\n[Sn, Ge]-UTL in calcined form experienced severe structural collapse\nduring an ultrasonic process under a pure water medium due to the\neasily hydrolytic Ge–O linkages in double four-ring units.\nThe ultrasonic treatment also caused the irregular arrangement of\nnanosized Si-rich <i>cfi</i> (mono- and/or multi-) layers,\ninducing the stacking faults and generating abundant intracrystal\nmesopores after calcination. In addition, the neutral environment\nhad little adverse influence on the content of the tetrahedrally coordinated\nSn ions, irrespective of the extensive removal of Ge species. The\nresultant Sn-Meso-UTL catalyst favored the diffusion of bulky substrates\nand oxidants, improving the accessibility of Sn active sites and performing\nefficient catalytic activity in the Baeyer–Villiger oxidation\nof ketones with an inorganic hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) or organic <i>tert</i>-butyl hydroperoxide oxidant.\nFurthermore, high selectivity (95.4%) of the target ε-caprolactone\nproduct was obtained through optimizing the H<sub>2</sub>O<sub>2</sub>/cyclohexanone molar ratio (0.2) and reaction time (40 min), which\nwas excellent in comparison with the representative Sn-β-F catalyst.