Sn-Beta zeolite hydrothermally synthesized via interzeolite transformation as efficient Lewis acid catalyst

Abstract

An innovative hydrothermal synthesis strategy of heteroatom-containing zeolite, in this case Sn-Beta, via interzeolite transformation is reported in present study. To the best of our knowledge, this prepared Sn-Beta zeolite possesses the highest isolated Sn contents (3.03wt% or Si/Sn molar ratio of 63) in comparison to other hydrothermally synthesized ones. The success of this synthesis strategy to Sn-Beta synthesized from MWW silica is mainly due to its nucleating and growing readily compared with those prepared from amorphous silica source. The introduction of Beta seeds and the structural similarity between the parent zeolite (MWW) and the targeted zeolite (*BEA) are found to be indispensable factors in the crystallization of Sn-Beta zeolite. The obtained Sn-Beta zeolites possess isolated tetrahedral Sn4+ in the framework and high hydrophobicity. Additionally, lowering the molar ratio of H2O2 to cyclohexanone and moderately reducing reaction time are proved to be effective methods to improve the selectivity of ε-caprolactone in the Baeyer–Villiger oxidation of cyclohexanone with H2O2 using Sn-Beta as Lewis catalyst. Thus, the prepared Sn-Beta zeolite demonstrated promising catalytic properties, especially for the desired products selectivity, in the Baeyer–Villiger oxidation of ketones as well as the isomerization–esterification reaction of dihydroxyacetone in ethanol, far outperforming the conventional Sn-Beta-F catalyst, which were attributed mainly to its high Sn content in the framework and excellent diffusion properties resulting from the relatively small crystal size.