Multinuclear MAS NMR identification of fluorine species on the surface of fluorinated γ-alumina

The fluorination on the gamma-alumina surface was studied by multinuclear MAS NMR and BET measurements. The fluorine species on the fluorinated gamma-alumina can be identified by F-19 MAS NMR combined with H-1 MAS NMR and Al-27 MAS and CP/MAS NMR. As proven by H-1 MAS NMR, fluorination of the alumina preferentially replaced the basic hydroxyl groups. Quantitative analysis showed that, at lower fluoride loadings, one alumina. hydroxyl is substituted by one fluoride without breaking the bridging Al-O-Al bonds. At high, fluoride content, more of the acidic hydroxyl groups are displaced by fluorine, and the number of added fluorine atoms exceeds the number of lost hydroxyl groups. Bridging Al-O-Al bonds are broken at high fluoride loading, and isolated AlxFy.nH(2)O fractions appear as observed by F-19 MAS and Al-27 MAS NMR. Three types of fluorine species were detected in the 19F MAS NMR spectra of the fluorinated gamma-alumina, which could be assigned to the fluorine species bound to one, two, and three octahedral aluminum atoms.