For the aqueous-phase hydrodeoxygenation (APHDO) of carboxylic acids over the Ru/C, Ru/ZrO 2 and Ru/Al 2O 3 catalysts, the C O hydrogenation and C–C bond cleavage reactions were studied by collecting reaction kinetics data and the measures of DRIFTS. The C–C bond cleavage was improved at high temperature and with high metal loadings. The acidic supports in combination with Ru metal can favor the C O hydrogenation of carboxyl. The C–C bond cleavage derived from the decarbonylation of acyl on the catalyst was studied by the measures of DRIFTS. The APHDO and DRIFTS results demonstrated that the C–C bond cleavage was favored in the order of Ru/C > Ru/ZrO 2 > Ru/Al 2O 3. The catalysts were characterized by multiple methods (H 2-TPR, NH 3-TPD, CO-FTIR and DRIFTS of propanoic acid). It is concluded that the effect of support on the reaction routes may be attributed to these factors of catalysts, i.e., surface acidity, metal–support interaction and electronic state of Ru species.