Composite oxides may have properties different from individual oxides. This corresponds to a more complex interfacial behavior of adsorbates (such as water, hydrogen，small molecule organics, etc) on the surface of mixed oxides. Thus dynamics and mechanism of reactantscan can be strongly influenced . It is evident that investigations of the properties of surface hydroxyls and coordination unsaturated metal atom on the oxide surface are of importance for detailed characterization of complex oxide materials and better understanding of the interfacial phenomena occurring on their surface. Solid-state NMR is effective to probe each of these characteristics. And its sensitivity to local geometry and coordination environments provides advantages over many more traditional characterization methods. The most widely employed tool to probe the surface structure of oxide catalysts is CP MAS NMR, in particular CP from hydrogen to the nucleus of interest. In addition, probe molecules can also be used to probe acid sites of oxides.
ssNMR was applied to compare the properties of ZnGa2O4with those of the corresponding individual oxides (such as ZnO, Ga2O3, etc) and ZnGa2O4with different morphology. Different probe molecules (such as TMP, TMPO) were used to characterize the acid-alkaline and active sites on the surface of the oxide. And ex-situ NMR experiments have been successful to detect the reaction intermediates and explore the reaction mechanism. It can be seen that the intermediates depend highly on the components and morphology of the oxides.
