Induced heterogeneity at the surface of group 4 dioxides as revealed by CO adsorption at room temperature

Abstract

Infrared, volumetric and calorimetric data for TiO₂, ZrO₂ and HfO₂, variously pretreated, are reported and discussed. Two types, at least, of M⁴⁺ sites are potentially present on all oxides, differing by the degree of coordinative unsateration. Surface impurities may alter or suppress them. Besides this structural heterogeneity, transmission of electronic effects through the solid induces heterogeneity during adsorption (shift of CO stretching frequency with coverage). The two phenomena are strictly related: the same relationship is proposed for the changes in absorption coefficient with peak position. This allows a new way of decomposing overall isotherms into individual contributions.