LOW-TEMPERATURE CO-2 ADSORPTION ON METAL-OXIDES - SPECTROSCOPIC CHARACTERIZATION OF SOME WEAKLY ADSORBED SPECIES

Carbon dioxide adsorption at temperatures between 173 K and 273 K on metal oxides such as MgO, Fe2O3, TiO2, ZrO2 and Al2O3 produces two types of weakly adsorbed species. Linearly coordinated CO2 is characterized by a shift up of the nu-3 vibrational mode and by the activation in IR and the slight shift down of the nu-1; 2-nu-2 Fermi resonance doublet. Bent CO2 species are characterized by a couple of strong bands in the regions 1900-1650 cm-1 and 1320-1150 cm-1, respectively. Weaker bands are also evident below 1000 cm-1 on oxides that allow the inspection of this region. Species thought to be side-on bonded on cationic sites are observed on all surfaces, while species thought to be C-bonded CO2- are also observed on TiO2 and ZrO2. Bent adsorbed CO2 is a likely intermediate in the formation of surface carbonate and bicarbonate species.