Adsorption of valeric acid and 5-nonanone on zirconia was investigated by DRIFTS and UV-vis DRS methods. Physical adsorbed and chemisorbed acid and ketone species have been found. Based on the experimental data obtained in this work and on DFT calculations reported in the literature two beta-ketoacid routes depending on surface carboxylate intermediates were proposed: (i) via interactions of surface monomolecular monodentate valerate with either monomolecular bridging bidentate or chelating bidentate and (ii) via interactions of two monodentates coordinated to the same Zr cation. The relative contribution of each of them in the overall ketone formation over metal oxide surfaces depends on the reaction conditions. (c) 2013 Elsevier B.V. All rights reserved.