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

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 mmolSn·gzeolite–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 mol2-Ad·molSn–1·h–1.