A thorough investigation of the catalysts Mo1Te1Ox/SiO2 and Mo1Bi0.05Te1Ox/SiO2 in the partial oxidation of propane is presented in this paper, in order to elucidate the nature and behavior of the active surface. The catalysts' structures and redox properties were investigated by means of X-ray powder diffraction, Raman spectroscopy, in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and H-2-TPR techniques. The results indicate that Te-polymolybdate is the main active phase on fresh catalysts. During reaction, the catalysts underwent a progressive reduction, resulting in the reconstruction of the active surface and the formation of a MoO3 phase. The synergistic effect between Te-polymolybdate and MoO3 was assumed to promote catalytic performance. The different stabilities of Mo1Te1Ox/SiO2 and Mo1Bi0.05Te1Ox/SiO2 catalysts are also discussed. Crown Copyright (C) 2010 Published by Elsevier B. V. All rights reserved.