In recent years, various protocols on preparing Lewis acidic Sn-β zeolite hydrothermally and postsynthetically have been reported. However, very little is known about the effects of different synthesis protocols on the Sn(IV) 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 different119Sn-NMR spectra, suggesting different Sn site speciation. Among postsynthetically prepared Sn-β zeolites, less variation in the resulting119Sn-NMR spectra have been observed, indicating a more reproducible synthesis procedure compared to hydrothermal synthesis in fluoride media. This work highlights the importance of119Sn-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.
Bibliographical noteFunding Information:
ETH acknowledges the SNF for the 600?MHz DNP spectrometer (206021_150710) and funding for W. C. L. (200020_149704), M. V. (200021_143600) and P. W. (200021_146661). We acknowledge Dr. David Gajan for the assistance on the measurements on the 400?MHz DNP spectrometer. Purdue University acknowledges Cindy Tavera (Universidad Nacional de Colombia) for assistance with sample preparation, and financial support provided by the Purdue Process Safety and Assurance Center (P2SAC). P. F. acknowledges FiSCH SBO ARBOREF. TU Eindhoven acknowledges Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), an NWO Gravitation programme funded by the Ministry of Education, Culture and Science of the Government of the Netherlands. The authors thank Prof. Lyndon Emsley and Dr. Anne Lesage for helpful discussions and for providing measurement time at their institution.
- Lewis acid