Efficient Construction of Framework Sn Sites over SnBeta Nanocrystals for Selective Oxidation

Abstract

SnBeta nanocrystals, i.e., SnBeta zeolite with a crystal size of ∼20 nm, high framework Sn content (∼2.2 wt %), and enhanced active site accessibility, were prepared by liquid grafting of SnCl₄·5H₂O onto dealuminated SiBeta in dimethyl sulfoxide (DMSO) solution. The use of β nanocrystals with high Al content as a precursor provided enhanced mass transportation and abundant silanol nests (after dealumination) for Sn anchoring, while the reaction at 413 K in DMSO solution also facilitated the reaction between SnCl₄ and silanols, thus substantially promoting Sn utilization efficiency. Specifically, a high framework Sn content of up to 1.0 wt % was obtained with a Sn utilization efficiency above 60% at a low Sn feeding of 0.14 mmol_Sn·g_zeolite^–1. Moreover, all samples with Sn contents ranging from 0.4 to 2.2 wt % showed identical active Sn structure, resulting in similar intrinsic activity toward Baeyer–Villiger oxidation of 2-adamantanone, with turnover frequencies approaching 62–72 mol_2-Ad·mol_Sn^–1·h^–1.