Physiochemical Properties of γ-Al2O3-MgO and γ-Al2O3-CeO2 Composite Oxides

A series of γ-Al2O3-MgO and γ-Al2O3-CeO2 composite oxides with different respective MgO and CeO2 loadings were prepared successfully via wet impregnation method. The synthesized composite oxides were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy-energy dispersive X-ray analysis (FESEM-EDAX), thermogravimeric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF) and Brunauer-Emmett-Teller (BET) methods. The point of zero charge (PZC) of oxides/mixed oxides was determined by salt addition and potentiometric methods to explore the effects of MgO and CeO2 contents on the PZC of γ-Al2O3. The results showed that, as the MgO loading was increased, PZC of alumina also increased linearly. However, in the case of CeO2 addition, the change in PZC of γ-Al2O3 was not so significant.
Moreover, the PZC of these synthesized composite oxides varied between the PZCs of pure oxides of Al2O3, MgO, and CeO2. Further, it was noted that, at lower MgO and CeO2 loadings, the structure of γ-Al2O3 was protected; however, at higher loadings, a change in the structure of γ-Al2O3 was observed. XPS results showed that binding energies decreased as MgO and CeO2 loadings were increased. This decrease in the binding energies of Mg and Ce was attributed to the change in their chemical environment
which caused change in the average valence state (oxidation state) of elements.