Dependence of ε-caprolactone selectivity on diffusion performance over Sn-Beta zeolite catalyst for Baeyer-Villiger oxidation of cyclohexanone

Sn-containing zeolite catalysts exhibit the unique feature of selectively activating carbonyl groups in organic compounds, which demonstrate relatively high activity and selectivity in the Baeyer-Villiger (B V) oxidation of aldehydes or ketones using H 2 O 2 as the oxidant. However, the influence of diffusion property and trace water on the ε-caprolactone selectivity as targeted product in the cyclohexanone's B V oxidation system with the green oxidant of aqueous H 2 O 2 remains unclear. To address this, three kinds of Sn-Beta zeolites are prepared by interzeolite transformation, structural reconstruction, and post-synthesis method to establish structure-property relationships. The physicochemical property and Sn coordinated state are investigated in detail. The existence of trace water in the reaction system negatively affects the conversion and product selectivity by competitive adsorption of water with reaction substrates and facilitated hydrolysis of ε-caprolactone, respectively. DFT calculation implies that kinetics dominates the conversion of cyclohexanone → ε-caprolactone → 6-hydroxycaproic acid. The structure-property relationship indicates that the cyclohexanone conversion and ε-caprolactone selectivity are closely related to the adsorption amounts of substrates and the diffusion performance of products, respectively, over Sn-Beta zeolite catalysts. Finally, the reusability and deactivation mechanism are analyzed. This study aims to provide guidance for designing efficient stannosilicate zeolite catalysts for B V oxidation through precisely modulating the zeolite's diffusion property.