In this work nanostructured CeO₂-ZrO₂-Sc₂O₃ mixed oxides prepared by citrate complexation method are studied. The effects of the co-substitution of ZrO₂ and Sc₂O₃ in the CeO₂ lattice are assessed in terms of the reducibility of the samples and their catalytic activity towards oxidation of methane. In situ X-ray absorption near edge structure (XANES) and X-ray powder diffraction (XPD) experiments with synchrotron light were performed to study the oxygen exchange capacity of these ternary oxides in reaction conditions and their structure stability. Catalytic experiments for complete methane combustion indicated a superior performance of samples containing Sc₂O₃ compared to the CeO₂-ZrO₂ one in terms of reaction onset temperature, conversion values and activation energy. Samples with 4 at% and 6 at% Sc doping exhibited a stable behavior at 800 °C during 7.5 h on-stream experiments. Structural stability was confirmed by in-situ XPD experiments with no secondary phase segregation or carbon deposition in reaction conditions.