| Summary: | In our previous study, we elaborated a method of determination of concentrations of the basic sites O<sup>2−</sup> and OH<sup>−</sup> in a quantitative IR study of CO<sub>2</sub> adsorption. Previous adsorption studies or TPD experiments only provided the total basicity without distinguishing between O<sup>2−</sup> and OH<sup>−</sup>. In this study, we determined the concentration of O<sup>2−</sup> and OH<sup>−</sup> on ZnO, Ga<sub>2</sub>O<sub>3</sub>, and MgO surfaces. The basicity of ZnO and MgO was found to be significantly higher than that of Ga<sub>2</sub>O<sub>3</sub>. The surface of ZnO was rich in O<sup>2−</sup>, the contribution of OH<sup>−</sup> was very small, and the Ga<sub>2</sub>O<sub>3</sub> surface contained mainly OH<sup>−</sup>. For MgO, the contribution of O<sup>2−</sup> and OH<sup>−</sup> was comparable. According to the IR results, only a small fraction of all surface hydroxyls were sufficiently basic to react with CO<sub>2</sub>. The partial dehydroxylation changed the proportion of the concentrations of O<sup>2−</sup> and OH<sup>−</sup> on the oxides. We also elaborated upon a new method to determine the total concentration of basic sites via CO<sub>2</sub> desorption monitored using IR. For all the oxides, we studied the sum of the concentrations of O<sup>2−</sup> and OH<sup>−</sup>, as determined in our quantitative IR studies, to find whether they were comparable with the total basicity determined in the desorption experiments.
|
|---|