Synthesis of CeO2–MnOx mixed oxides and catalytic performance under oxygen-rich condition

Ce0.5Zr0.5O2, Ce0.5Zr0.2Mn0.3O2 and Ce0.5Mn0.5O2 were prepared by citric acid sol–gel method. The effect of manganese on the structural and redox properties of ceria-based mixed oxides was investigated by means of powder X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller analyses, temperature-programmed reduction and catalytic activity evaluation in the presence of excess O2. The results showed that some Mn cations could enter into the ceria lattice to form solid solutions. Mn3O4 appeared due to the instability of the mixed oxides with increment of the Mn doping ratio while another oxide Mn2O3 is detected in the physical mixture of ceria and manganese oxide. These Mn-doped mixed oxides, especially Ce0.5Mn0.5O2, presented better catalytic activities than Ce0.5Zr0.5O2 and even Pt-loaded catalyst for total oxidation of C3H8 and oxidative sorption of NO in the presence of excess oxygen. The oxidation ability of Mn and the strong interaction between Mn and Ce were suggested to promote the oxygen storage/transport capacity of the mixed oxides as well as reactive adsorption of nitric oxide and hydrocarbons.