The structure of adsorbed nitrate in thoria sols and gels

The structure of the adsorbed nitrate group in thoria sols and gels has been studied by i.r. spectroscopy. Spectra are interpreted as showing that in sols nitrate is adsorbed as the nitrate ion and in gels as a unidentate nitrate surface group. With further loss of water on heating in a vacuum transition to a bidentate nitrate structure occurs. Desorption of nitrate is complete in a vacuum at 400°C; a residual adsorbed unidentate carbonate species remains.