Hierarchical Sn-BEA Zeolites in Catalytic Oxidation of Dihydrocarvone with Hydrogen Peroxide

The study proposes a novel method for synthesizing hierarchical Sn-BEA zeolites. This method consists of two successive steps: dealumination of a hierarchical Al-BEA zeolite prepared in a pre-concentrated reaction mixture; and incorporation of Sn by impregnating the dealuminated zeolite with a tin(IV) chloride ethanol solution. In the hierarchical zeolites, the Si/Sn ratio was varied between 29 and 41 by adding different amounts of the tin salt to the impregnating solution. The samples were tested in the Baeyer–Villiger catalytic oxidation of dihydrocarvone with hydrogen peroxide. The initial dihydrocarvone consumption rate has been found to increase with the concentration of Lewis acid sites in the samples and exceed that of the microporous Sn-BEA zeolite synthesized by a similar procedure except for the absence of the pre-concentration of the mixture. The highest yield of lactone (47%) has been achieved in the presence of the hierarchical Sn-BEA sample with the highest concentration of strong Lewis acid sites.