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

Abstract

Various CeO2–MxOy (MxOy = 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 Ce0.5Zr0.5O2 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.