Solid state <sup>1</sup>H NMR results have shown, for the first time, a stable and highly deshielded protonic species at 12-15 ppm in zeolite HZSM-5 that is significantly downfield of the 4.2 ppm shift for known Brønsted acid protons. In addition, direct evidence has shown that some EFAl (extra framework aluminum) species exhibit acidic behavior. Spin-lattice relaxation, chemical exchange, and SEDOR (spin echo double resonance) experiments strongly suggest that the 12-15 ppm peak corresponds to EFAl species proximate to framework Al atoms. Brønsted/Lewis synergisms and other possible explanations are proposed for its origin.

Direct detection of multiple acidic proton sites in zeolite HZSM-5

255th National Meeting (2018)

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