Ethoxy Groups on ZrO₂, CuO, CuO/ZrO₂ Al₂O₃, Ga₂O₃, SiO₂ and NiO: Formation and Reactivity

The reaction of ethanol with surface OH groups on ZrO₂, CuO/ZrO₂, CuO, Al₂O₃, Ga₂O₃, NiO, and SiO₂ was studied by IR spectroscopy. The basicity of oxides was followed by CO₂ adsorption, and their ability to oxidize was investigated by H₂-TPR. It has been found that ethanol reacts with surface OH groups forming ethoxy groups and water. Some oxides: ZrO₂, CuO/ZrO₂, Al₂O₃, and Ga₂O₃ contain several kinds of OH groups (terminal, bidentate, and tridentate) and terminal hydroxyls react with ethanol in the first order. Two kinds of ethoxyls are formed on these oxides: monodental and bidental ones. On the other hand, only one kind of ethoxy group is formed on CuO and NiO. The amount of ethoxy groups correlates with the basicity of oxides. The biggest amount of ethoxyls is produced on the most basic: ZrO₂, CuO/ZrO₂, and Al₂O₃, whereas the smallest amount of ethoxyls is produced on CuO, NiO, and Ga₂O₃, i.e., on oxides of lower basicity. SiO₂ does not form ethoxy groups. Above 370 K ethoxy groups on CuO/ZrO₂, CuO, and NiO are oxidized to acetate ions. The ability of oxides to oxidize ethoxyl groups increases in the order NiO < CuO < CuO/ZrO₂. The temperature of the peak in the H₂-TPR diagram decreases in the same order.