Multinuclear MAS NMR Identification of Fluorine Species on the Surface of Fluorinated γ-Alumina

The fluorination on the γ-alumina surface was studied by multinuclear MAS NMR and BET measurements. The fluorine species on the fluorinated γ-alumina can be identified by 19 F MAS NMR combined with 1 H MAS NMR and 27 Al MAS and CP/MAS NMR. As proven by 1 H 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 Al x F y · n H 2 O fractions appear as observed by 19 F MAS and 27 Al MAS NMR. Three types of fluorine species were detected in the 19 F MAS NMR spectra of the fluorinated γ-alumina, which could be assigned to the fluorine species bound to one, two, and three octahedral aluminum atoms.