Rapid Synthesis of Hierarchical Sn-Beta-Hie Zeolite as an Efficient Lewis Acid Catalyst

Stannosilicates Sn-beta with open pore spaces (e.g., mesopore system) have always been significantly expected for the liquid-phase transformation of ketones into esters. In this present study, a structural reconstruction route with the assistance of polydiallydimethylammonium chloride (PDDA) is proposed to synthesize the hierarchical Sn-Beta-Hie catalyst. The dealuminated beta (beta-DA) zeolite was first degraded to form Beta debris (Si source), which was then rapidly self-assembled to Sn-containing zeolite with tin(IV) chloride pentahydrate (SnCl4·5H2O) during 12 h. In particular, the addition of organic directing agents PDDA under the crystallization systems created abundant mesopores in the framework. The resultant Sn-beta-Hie catalyst with more open channels facilitated the diffusion of molecules and enhanced the accessibility of Sn active centers, performing efficient catalytic ability for Baeyer–Villiger oxidation of ketones irrespective of the types and sizes of oxidants (e.g., hydrogen peroxide, H2O2; tert-butyl hydroperoxide). Moreover, the target ε-caprolactone selectivity reached up to 97.2% by adjusting precise the molar ratio of H2O2/cyclohexanone (0.2) as well as reaction time (1 h). The experiment results demonstrated that the hierarchical Sn-beta-Hie catalyst was more excellent in comparison to the typical Sn-beta-F catalyst.