The oxidation of methanol on iron-molybdenum catalysts was investigated with view of gathering information about catalyst deactivation at temperatures in the catalyst bed lower than 300 degrees C. A 15 months' industrial experiment was carried out and samples of spent catalyst discharged step by step from the reactors were characterized by Mossbauer spectrometry, XRD, chemical analysis and surface area measuring. Catalytic measurements were also performed using a pseudo-isothermal reactor under conditions close to the industrial experiment. The results obtained demonstrate that, although slower, the process of deactivation of the industrial catalyst takes place even at temperatures lower than 300 degrees C. We reached the conclusion that the main reason for this is the removal of a part of the MoO(3) and the decreasing of the specific surface. It was established that the formation of FeMoO(4) and Fe(2)O(3) is negligible and does not represent a dominant factor influencing the catalytic properties of the Fe-Mo catalyst under these conditions of industrial exploitation. (C) 2010 Elsevier B.V. All rights reserved.