Surface characterization of modified aluminas. Part 5.—Surface acidity and basicity of CeO2–Al2O3 systems

Abstract

The addition of CeO₂ to Al₂O₃ supports and Al₂O₃-based catalysts leads to improved performance, that can be explained by surface chemical rather than structural morphological effects. Surface characterization of CeO₂–Al₂O₃ systems has been carried out by in situ FTIR spectroscopy. The adsorption–desorption of pyridine as a surface probe allowed us to test for Brønsted acidity, never found, and the total Lewis acidity, which is higher for CeO₂–Al₂O₃ systems than for pure Al₂O₃ supports. Several types of surface centres of different acidity could be identified, mainly by testing the competitive adsorptivity towards CO after stepwise desorption of pyridine at various temperatures. The adsorption of CO₂ was used to test the basicity of CeO₂–Al₂O₃ systems. The presence of CeO₂, a basic oxide, does not modify appreciably the basic properties of Al₂O₃, on which a low concentration of rather weak basic centres is present, whereas the presence of Al₂O₃ tends to inhibit the high basicity typical of CeO₂.