LAUSR

Low-temperature 15N dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) of adsorbed pyridine in combination with FTIR measurements and DFT calculations was applied to investigate the surface sites of γ-alumina, which can be divided into four groups: (1) groups 1 and 2, associated with less shielded 15N chemical shifts and the lowest ν(8a) frequencies of adsorbed pyridine, corresponding to weakly adsorbed H-bonding pyridine to hydroxyl group or chemisorbed water on alumina; (2) group 3, with intermediate 15N chemical shifts and ν(8a) frequencies, corresponding to pyridine coordinated to specific Lewis acid sites, namely five-coordinated (AlV) aluminum atoms of the (100) facet, as well as some H-bonded pyridine; (3) group 4, associated with the most shielded 15N chemical shift and the highest ν(8a) frequency, selectively assigned to Lewis acid Al sites located on the (110) facet and corresponding to both four- and five-coordinated aluminum atoms (AlIV and AlV). Noteworthy, a correlatio...