Single step synthesis of nanosized CeO₂–M_xO_y mixed oxides (M_xO_y = SiO₂, TiO₂, ZrO₂, and Al₂O₃) by microwave induced solution combustion synthesis: characterization and CO oxidation

Various CeO₂ –M_xO_y (M_xO_y = SiO₂, TiO₂, ZrO₂, and Al₂O₃) mixed oxides were prepared by microwave induced solution combustion method and analyzed by different complimentary techniques, namely, X-ray diffraction (XRD), Raman spectroscopic (RS), UV–Vis diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG-DTA), and BET surface area. XRD analyses revealed that CeO₂ –SiO₂ and CeO₂ –TiO₂ mixed oxides are in slightly amorphous form and exhibit only broad diffraction lines due to cubic fluorite structure of ceria. XRD lines due to the formation of cubic Ce_0.5Zr_0.5O₂ were observed in the case of CeO₂ –ZrO₂ sample. RS results suggested defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The UV-DRS measurements provided valid information about Ce⁴⁺ ← O²⁻ and Ce³⁺ ← O²⁻ charge transfer transitions. XPS studies revealed the presence of cerium in both Ce³⁺ and Ce⁴⁺ oxidation states. The ceria–zirconia combination exhibited better oxygen storage capacity (OSC) and CO oxidation activity when compared to other samples. The significance of present synthesis method lays mostly on its simplicity, flexibility, and the easy control of different experimental factors.