Nuclear magnetic resonance investigation of fluorinated oxide catalysts

Pulsed nuclear magnetic resonance (NMR) techniques have been used as direct spectroscopic probes of the local chemical environments of the hydroxyl groups and fluorine atoms of fluorinated silica. Hydroxyl groups and fluorine atom concentrations were obtained from NMR data. The line shapes of the hydroxyl group spectra are narrow (<3 kHz) and asymmetric. The fluorine spectra can be described by isolated SiF groups. The anisotropy of the fluorine chemical shift powder pattern is 96 ppM. The hydroxyl groups do not exist as closely spaced pairs. The same is true of the fluorine atoms. Fluctuations occur in the local magnetic fields of the nuclei. The changes that occur in the line shapes of the hydroxyl group and fluorine spectra when observed at various temperatures depend upon the concentration of the surface species and upon the calcining temperature