Acid–base properties of alumina–magnesia mixed oxides. Part 4.—Infrared study of adsorption of carbon dioxide

Abstract

The adsorption of CO₂ on alumina, alumina–magnesia mixed oxides and magnesia has been studied by means of i.r. transmission absorption spectroscopy. CO₂ was found to be weakly adsorbed on accessible cations. With high densities of surface hydroxyl groups lateral interactions of these cationicly bound CO₂ molecules with hydroxyl groups have also been observed. Several surface carbonates were formed and were identified as bicarbonates and monodentate, bidentate and ionic carbonates. The wavenumbers of the symmetric stretching vibration of the surface bicarbonates and the wavenumber difference of the symmetric and antisymmetric stretching vibration of the monodentate carbonates decreased with increasing content of MgO in the mixed oxides.