Facile Synthesis of Hierarchical Sn‐Beta Zeolite by Tuning Chemical Equilibrium of Fluoride Etching.

The Sn‐Beta zeolite is commonly known as a unique Lewis acid catalyst, however, usually suffers from the drawback of diffusion limitation within zeolitic micropores. To address these issues, the present work reports a facile fluoride etching approach for the synthesis of hierarchical Sn‐Beta zeolites by tuning chemical equilibrium of HF and NH4F mixed solutions. It was found that the etching of HF solution alone only extracts Sn species in the Sn‐Beta framework while adding NH4F into HF solution shifts the chemical equilibria to produce more reactive HF2− for Si, thereby achieving unbiases selective extraction of Si and Sn from *BEA framework. The obtained hierarchical Sn‐Beta zeolite possessed excellent catalytic activity in Baeyer‐Villiger oxidation of bulky 2‐adamantanone with aqueous hydrogen peroxide. Structure‐performance relationship revealed that the Lewis acid site and the pore structure are two crucial factors determining the catalytic activity. The former was identified as a catalytic active center while the latter increase the accessibility to active sites in microporous Sn‐Beta zeolites by forming hierarchical porosity. Therefore, the sample obtained after optimizing the conditions of NH4F‐ HF mixed solutions presented a remarkably enhanced catalytic oxidation activity for bulky molecules. [ABSTRACT FROM AUTHOR]