Vibrational and thermodynamic features of CO adsorbed onto Al2O3 and Ca-doped Al2O3

Infrared and microcalorimetric data for the adsorption of CO onto a CaO/Al2O3 system are reported, and related to the adsorption on pure Al2O3. The CO/Al2O3 system is severely modified, as Ca2+ ions accumulate at the surface of alumina, favouring the occupation of regular crystallographic terminations and gradually converting them into a bidimensional Ca aluminate layer. Unlike unsupported CaO, CaO/Al2O3 adsorbs CO as linear complexes σ-coordinated onto coordinatively unsaturated Ca2+ ions. Spectral and thermodynamic features of the CO/Ca2+ complexes agree with the behaviour previously postulated for CO on non-d metal oxides.