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 19F MAS NMR combined with 1H
MAS NMR and 27Al MAS and CP/MAS NMR. As proven by 1H 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
Fy·nH2O fractions appear as observed by 19F MAS and 27Al MAS NMR.
Three types of fluorine species were detected in the 19F 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.
Detailed adsorption thermodynamic data of organosulfur and organonitrogen molecules on NiMoS hydrotreating catalyst active sites were studied by density-functional theory (DFT) calculations. Initially, the adsorption of the molecules on the NiMoS edge surface is studied, and the most stable configuration for each molecule is identified. The changes in electronic energy and zero point vibrational energy upon the adsorption of different molecules on the NiMoS surface are calculated. The contribution of adsorbed molecules, as well as gas phase molecules, to changes in entropy and C p values are obtained by calculating vibrational frequencies of adsorbed and free molecules. With these data, the changes in enthalpy, entropy, and free energy due to the adsorption on the NiMoS edge surface at different temperatures are determined. These data can be used to estimate the relative surface coverage of each type of species at different reaction conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.