Different VOx/TiO2 catalyst have been catalytically tested and studied by in situ-spectroscopic methods (FT-IR, UV/vis, EPR) in the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid (AcOH). While 1-butene OHS follows the sequence butene -> butoxide -> ketone -> AcOH/acetate with a multitude of side products also formed, n-butane OHS leads to AcOH, COx and H2O only. Water vapour in the feed improves AcOH selectivity by blocking adsorption sites for acetate. The admixture of Sb2O3 was found to improve AcOH selectivity which is due to deeper V reduction under steady state conditions and lowering of surface acidity. VOx/TiO2 catalysts with sulfatecontaining anatase are the most effective ones. Covalently bonded sulfate at the catalyst surface causes specific bonding of VOx, stabilizes active V species and ensures their high dispersity. (c) 2005 Elsevier B.V. All rights reserved.