Two alumina-supported Ce/Pr mixed oxides, with different alumina promoters, La and Si, have been investigated in this paper. A gradual decrease of the Oxygen Storage Capacity (OSC) was observed after reducing the samples at progressively higher temperatures. However, depending on the nature of the alumina promoter, the temperature at which the loss of OSC started to be evident changed, being higher in the La-doped sample. A structural characterization study by X-ray diffraction (XRD) of the samples submitted to different reduction and reoxidation treatments in a range of temperatures was performed. From this study a correlation between the nature of the observed phases, the alumina promoter, and the deactivation behaviour could be stated. FTIR study is of particular interest because the observed correlation between the reduction degree and the position and intensity of the FTIR band is altered when deactivation phenomena appear. (C) 2011 Elsevier B.V. All rights reserved.