The present work focuses on the partial oxidation of methyl ethyl ketone to acetic acid over TiO2 supported vanadia catalysts with V loadings from 1 to 13.5 wt.%. In order to elucidate the relation between catalytic activity and the structure of the catalysts, the catalysts were also characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction with hydrogen (TPR), and temperature programmed desorption of lattice oxygen (TPD-O-2). The investigations show that with increasing V loading the MEK conversion increased whereas the turn-over frequency decreased. At lower V loading (1-4 wt.%) the total oxidation to COx was favoured and the selectivities to acetic acid and other oxygenated products were low. The highest selectivities to acetic acid were achieved at V loadings of 4-6 wt.%. Based on literature data and our results, a scheme of the reaction pathways for the partial oxidation of MEK to AcOH and other by-products was developed. (C) 2007 Elsevier B.V. All rights reserved.