The electrooxidation of ethanol on carbon supported PtRuMo nanoparticles of different Mo compositions has been studied in the temperature range of 30-70 degrees C. Current-time curves have shown an increase of the current density with the Mo introduction during the ethanol oxidation at 0.5 V in a whole temperature range. The incorporation of different amount of MoOx (similar to Mo5+) like species over PtRu systems produces ternary catalyst with similar structural characteristics as particle size or crystal phases, but the catalytic behavior depended on both the surface amount of Mo and on the applied potential. In situ spectroelectrochemical studies have been used to identity adsorbed reaction intermediates and products (in situ Fourier transform infrared spectroscopy, FTIR) and volatile reaction products (differential electrochemical mass spectrometry, DEMS). For all catalysts, incomplete ethanol oxidation to C2 products (acetaldehyde and acetic acid) prevails under the conditions selected in this study. The higher CO tolerance of PtRuMo/C catalysts at very low potentials (<0.3 V) results to minimum or no CO poisoning of the Pt and Ru surfaces, in contrast to the PtRu/C catalyst, which are rapidly blocked by CO. Therefore, catalyst with higher amount of Mo allows a fast "replenishment" of the active sites leading to the formation of acetaldehyde and, especially, acetic acid at potentials above 0.3 V. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.