COPPER OXIDE SUPPORTED ON ALUMINA .3. X-RAY K-ABSORPTION EDGE STUDIES OF CU2+ SPECIES

X-Ray K-absorption edge spectroscopy studies were performed on samples containing cupric ion supported on γ-alumina. It was found that, at lower concentrations of cupric ion, a surface phase is present that resembles the structure of copper aluminate. Parameters that affect the formation of this aluminate phase include the surface area of the alumina and the concentration of cupric ions. The aluminate phase is undetectable by X-ray diffraction. It is proposed that the aluminate surface phase accounts for the sharp rise in magnetic susceptibility that has been previously noted in the susceptibility isotherm of the system copper oxide-on-alumina. When samples containing the aluminate surface phase are reduced and reoxidized in the absence of moisture, the aluminate is converted to cupric oxide. Three distinguishable phases have now been identified in composites containing cupric ions dispersed on alumina: isolated cupric ions, a copper aluminate surface phase, and cupric oxide. The chemical bonds in the first two phases are apparently the same, and different from those in the third one. © 1969.