Selective active site placement in Lewis acid zeolites and implications for catalysis of oxygenated compounds
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d0sc03809a.pdf
Description
Published version
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1.28 MB
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Checksum (MD5)
d79ef8a3ecc32094e55cb4b4791c1cef
Author(s)
Rodríguez-Fernández, Aída
Di Iorio, John R
Paris, Cecilia
Boronat, Mercedes
Corma, Avelino
Román- Leshkov, Yuriy
Moliner, Manuel
Date Issued
2020
Journal
Chemical Science
Publisher
Royal Society of Chemistry (RSC)
Version
Final published version
Abstract
© The Royal Society of Chemistry. The selective incorporation of isolated framework Lewis acid sites at specific crystallographic positions in high-silica zeolites was achieved by applying a rationalized post-synthetic grafting methodology. The removal of framework Ge atoms from a Ge-BEC zeolite with low concentrations of Ge in the framework (Si/Ge ∼ 150) followed by grafting allows the synthesis of Sn-BEC zeolites with Sn atoms positionally biased into the double-4-ring (D4R) crystallographic positions of the BEC framework. Spectroscopic characterization using solid-state nuclear magnetic resonance (NMR) coupled with theoretical calculations revealed that Sn atoms preferentially form open Sn sites in the D4R of Sn-BEC. This observation was supported by IR spectra of adsorbed deuterated acetonitrile (CD3CN), a known titrant of Sn sites in zeolites. The catalytic implications of selective incorporation of open Sn sites in Sn-BEC were probed using the Meerwein-Ponndorf-Verley-Oppenauer (MPVO) reaction. Although the MPVO turnover rates normalized by the total number of open Sn sites were comparable on Sn-BEC and a conventional Sn-Beta catalyst synthesized in fluoride media (Sn-Beta(F)), Sn-BEC demonstrated higher per gram reaction rates because of its larger fraction of open sites compared to Sn-Beta(F). These results highlight the advantage of placing active sites in targeted locations within a zeolite structure. The methodology presented here to selectively place catalytic active sites via sacrificial heteroatoms, such as Ge, can be generalized for the design of many other tetrahedrally-coordinated metal-containing zeolites. This journal is
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
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DOI of Published Version
https://doi.org/10.1039/D0SC03809A
