IR Studies of Ethoxy Groups on CeO₂

The reaction of ethanol with a surface of CeO₂ was studied using IR spectroscopy. In some experiments, CeO₂ was pretreated in a vacuum at 820 K which caused a partial reduction. In other experiments, CeO₂ was reduced with hydrogen at 770 K. We also used CeO₂ oxidized by oxygen treatment at 670 K. At low coverages, ethoxy groups and new surface OH groups were formed and water was not produced. On the other hand, at higher loading surfaces, Ce-OH was consumed and ethoxy groups and water were formed. Three kinds of ethoxyls were found on CeO₂: monodentate, bidentate, and tridentate ones. They were characterized by various frequencies of symmetrical, asymmetrical, and combinational bands of C-C-O units. The reduction of CeO₂ increased the contribution of tridentate ethoxyls and the oxidation increased the contribution of monodentate ones. At higher temperatures, ethoxy groups were oxidized to acetate ions with the formation of new surface OH groups. Monodentate ethoxyls were the most reactive and tridentate ones were the least reactive during oxidation. The amounts of acetate species were the highest for the oxidized CeO₂.