Identifying Sn site heterogeneities prevalent among Sn-Beta zeolites

In recent years, various protocols on preparing Lewis acidic Sn-β zeolite hydrothermally and post-synthetically have been reported. However, very little is known about the effects of different synthesis protocols on the SnIV speciation in the final material. Even the effects of individual synthesis parameters within a certain preparation method have not been studied systematically. Here, we demonstrate that hydrothermally synthesized Sn-β zeolites prepared via very similar recipes show significantly different 119Sn NMR spectra, suggesting different Sn site speciation. Among post-synthetically prepared Sn-β zeolites, less variation in the resulting 119Sn NMR spectra have been observed, indicating a more reproducible synthesis procedure compared to hydrothermal synthesis in fluoride media. This work highlights the importance of 119Sn NMR measurements to elucidate the precise local geometry of the Sn heteroatoms in Sn-β, and the need to quantify the number of reactive Sn sites on each sample that participate in a given catalytic reaction, in order to accurately compare materials prepared by different routes.