Acidity Strength of Solid Catalysts Probed by Hyperpolarized Natural Abundance 17 O NMR Spectroscopy.

Observation of Brønsted acid sites: By enhancing the solid-state NMR signals of 17 O at natural abundance with dynamic nuclear polarization (DNP), Pruski et al. were able to measure oxygen-proton distances accurately with sub-picometer precision. The results give insight into the Brønsted acidity of a range of solid acid catalysts.