An examination of alkali-exchanged BEA zeolites as possible Lewis-acid catalysts

• Alkali-exchanged BEA zeolites are shown to interact strongly with Lewis bases.
• Pyridine, acetonitrile, 2-methyl-2-propanol and CO interact most strongly with Li-BEA > Na-BEA > K-BEA.
• Alkali-exchanged BEA are not active for alcohol dehydration or reductive etherification of HMF.

The possibility of using alkali-exchanged BEA zeolites as Lewis-acid catalysts was examined using temperature-programmed desorption (TPD)/thermogravimetric analysis (TGA) measurements of adsorbed pyridine, 2-propanamine, diethyl ether, 2-methyl-2-propanol, and acetonitrile, FTIR of pyridine and CD3CN, calorimetry of CO, and reaction rates for reductive etherification of 5-hydroxymethyl furfural (HMF) with 2-propanol. Adsorption on the alkali cations occurs through ion–dipole interactions, as evidenced by the fact that adsorption is strongest on Li, followed by Na and K. Adsorption of all the probe molecules was much stronger on Li-BEA than on acid sites formed by framework Sn in SnBEA; however, the alkali-exchanged BEA samples were not catalytically active for alcohol dehydration or reductive etherification of HMF. The implications of these results for the characterization of solid Lewis acidity are discussed.

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