Design of transition and rare earth metal doped ceria nanocomposite oxides for CO oxidation

Nanocrystalline Ce x TM1−x O2 (TM = Zr4+ and Hf4+) and Ce x RE1−x O2−δ (RE = La3+, Pr3+/4+ and Tb3+/4+) solid solutions were prepared by modified coprecipitation method and thermally treated at two different temperatures, 773 and 1073 K in order to determine the thermal behaviour. The synthesized samples were studied in detail by means of N2 physisorption, XRD, Raman, X-ray photoelectron spectroscopy (XPS), and TEM/HREM techniques. The catalytic efficiency was performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. XRD results indicated the formation of transition and rare earth metal doped ceria solid solutions with typical fluorite like cubic structure. Raman spectra displayed the existence of oxygen vacancies. XPS measurements revealed that Ce, Pr and Tb are present in both 3+ and 4+ oxidation states, La in 3+ state, and Zr and Hf in 4+ state. Among the investigated samples, the catalytic measurements revealed that ceria–hafnia solid solution exhibits superior catalytic activity towards CO oxidation, which could be due to a high OSC and other favourable physicochemical properties.