Characterization of acid-base sites in oxides

The acidity and basicity of the oxides and metal oxide surfaces is one among the most peculiar properties of this group of inorganic products that have been exploited in catalysis from decades. The different types of oxides (single oxides, doped and modified oxides, supported oxides, mixed and complex oxides) are here described with emphasis on their acid-base functionalities in relation with the catalytic activity. The prediction of the acidity insurgence from the oxide composition is discussed. The possibility to have a deep knowledge of the amount of acid sites and of the acid strength and strength distribution at the oxide surface is here presented. Adsorption by suitable probes with basic/acidic characteristics can be realized in a microcalorimetry of adsorption giving information on the heterogeneity of the surface. Alternatively, probe desorption can be realized by a temperature increasing program to obtain the acid-site strength distribution. In any case, quantitative information on the acid oxide surfaces can be obtained with the relevant thermodynamic of kinetic parameters which determine the amount and strength of the acid sites.