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Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Zr-Site Lewis Acidity Determines Terpenoid Reduction Selectivity.
Kinga Gołabek1, Svetlana Kurucová1, Juan Francisco Miñambres1
1Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Albertov 6, Prague, Praha 128 43, Czech Republic.
Lewis acid zeolites, specifically Zr-beta, show distinct catalytic activities based on "open" versus "closed" Lewis acid sites. "Closed" sites favor Meerwein-Ponndorf-Verley reduction, while "open" sites promote cyclization, enabling targeted catalyst design.
Area of Science:
- Catalysis
- Materials Science
- Organic Chemistry
Background:
- Lewis acid zeolites, particularly Al-free Zr and Sn silicates, are effective catalysts for Meerwein-Ponndorf-Verley (MPV) reduction of carbonyl compounds.
- The precise role of different types of Zr sites (open vs. closed) in Zr-zeolites for chemoselective reduction and competing reactions remains unclear.
- Understanding site-specific catalysis is crucial for optimizing reactions like citronellal reduction, which can yield multiple products.
Purpose of the Study:
- To correlate the characteristics of Lewis acid sites in Zr-substituted beta and MFI zeolites with their catalytic selectivity.
- To elucidate the role of
Main Methods:
- Fourier transform infrared (FTIR) spectroscopy using deuterated acetonitrile and acetone to probe and differentiate between
Main Results:
- Zr-beta zeolites with a high concentration of
Conclusions:
- The Lewis acidity of Zr sites in zeolites dictates selectivity in terpenoid reduction.
- Weaker Zr-beta "closed" sites selectively catalyze MPV reduction of citronellal to citronellol.
- Stronger Zr-beta "open" sites preferentially catalyze intramolecular carbonyl-ene cyclization to isopulegol.
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