The use of vibrational spectroscopy in the surface characterization of microcrystalline oxides

A systematic investigation of the surface morphology and of the vibrational properties of CO adsorbed on several simple oxides with regular crystalline habit and exposing thermodynamically stable and neutral faces, is briefly reviewed with the aim to elucidate the spectroscopic manifestations of CO adsorbed on well-defined crystallographic positions; the cases of MgO and alpha-Cr2O3 are then discussed in more details. In order to have a better insight on the role of surface defectivity in catalytic reactions, the activity towards CO of perfect, low-index faces and of more defective situations (like those associated with edges, steps, corners) is also discussed. Finally, the experimental C-O stretching frequencies are compared with those calculated on the basis of the local electric field strengths at the adsorption sites.