The mechanism of the formaldehyde oxidation to formic acid on a V-Ti-O catalyst has been studied by pulse and spectrokinetic (in situ FTIR) methods. Bidentate symmetrical formates and asymmetric formates are observed by formaldehyde adsorption both in the presence and in the absence of dioxygen in the temperature range between 100 and 200 degrees C. Formic acid may form by two parallel pathways: by an associative mechanism through the oxidative elimination of bidentate formates and by a stepwise redox Mars-van Krevelen mechanism through the decomposition of asymmetric formates; the associative mechanism seems to be preferable. (c) 2006 Elsevier B.V. All rights reserved.