The conversion of propanoic acid under high hydrogen pressure has been studied over zirconia-supported monometallic Ru and bimetallic Ru-Mo catalysts. The cleavage of C-C bond of propanoic acid to methane and ethane is improved and the formation of C=O hydrogenation products (propanol and propane) is decreased with increasing the temperature. Upon addition of Mo, both the overall activity and the C-C bond cleavage selectivity decrease while the selectivity of C=O hydrogenation increases. With increase of Mo contents, the C-C bond cleavage reaction is significantly inhibited, especially at high temperature. This is also confirmed by the DRIFTS of propanoic acid, showing that the propanoyl intermediate species on Ru-Mo bimetal catalysts is more difficult to dissociate to CO compared with Ru monometal catalyst. Based on H-2-TPR, CO-FFIR and DRIFTS of propanoic acid characterizations, the reaction mechanisms and the resulting selectivity towards the possible reaction paths (C-C bond cleavage/C=O hydrogenation) are discussed in terms of the formation of Ru-MoOx and the stability and variety of propanoyl intermediate species occurring on the Ru-Mo bimetal catalysts. It is suggested that the interaction of Ru and MoOx species and the formation of Ru-MoOx interface are the important factors for the decrease in the TOF of propanoic acid and the C-C bond cleavage selectivity. (C) 2011 Elsevier B.V. All rights reserved.