Catalytic activity results of oxidative steam reforming of propane studied on Pd catalysts are here explained on the basis of different characterization analyses under reaction conditions. XRD in situ was applied to investigate nanostructure features by means of a Rietveld refinement giving additional information about ceria lattice parameter along the reaction. The refinement was applied in all pretreatment steps, after reduction and after reaction. A good correlation was obtained in all conditions. The mean crystallite sizes were calculated for CeO2, Pd-0 and NO at the higher intensity planes. Results of crystallite sizes after reaction during 1, 3, 8 and 20 h were determined. One can conclude that CeO2 enhances and maintains the dispersion of Pd on bulk catalyst and prevents Pd from severe aggregation along the reaction because no sintering was detected even after 20 h of reaction. The changes in lattice cell parameter determined by Rietveld refinement suggested high oxygen mobility inside the fluoritic structure, facilitating formation of CeO2-x species. DRIFTS were carried out under static and dynamic measurements and compared with TPD of propane in the presence of oxygen. These results showed formation of surface intermediate species (formates/carbonates) and CH. species on surface during the oxidative steam reforming of propane that allows proposing a surface reaction mechanism. (C) 2009 Elsevier B.V. All rights reserved.