We investigated the structure and interface of the Ni/Nb2O5 under different treatment conditions and its effect on the partial oxidation of methane. In situ investigation of the catalyst reduced in H-2 at different temperatures (300, 400 and 500 C-omicron) indicated the occurrence of SMSI effect for the sample reduced at the higher temperature, caused by either decoration and/or electronic factors, evaluated by CO chemisorption, X-ray diffraction, HRTEM and UV-vis diffuse reflectance spectroscopy. Under reaction conditions (CH4/O-2/N-2/Ar = 2/1/1/6, GHSV = 250 mLg(-1) h(-1)), the catalysts reduced at 300 and 400 C-omicron showed two nickel sites: NiNbO4 and NiNb2O6, which were active for syngas production (H-2 + CO). On the other hand, the catalyst reduced at 500 C-omicron showed, besides NiNbO4 and NiNb2O6, the Nb2O5/Ni delta+ site (where delta = 2 or 3) obtained from the reoxidation of NbOx species priorly generated by SMSI effect. We attribute the activity for methane coupling reactions to this Nb2O5/Nis(delta+) site (where delta = 2 or 3). (C) 2017 Elsevier B.V. All rights reserved.