The interaction of formaldehyde with Pt/TiO2 and Au/TiO2 catalysts was investigated at 300-473 K by Fourier transform infrared spectroscopy and mass spectrometry. The effects of the pretreatments and the metal content of the catalysts, as well as the effects of the reaction temperature on the formation of the surface species and on the gas phase products were studied. Molecularly adsorbed formaldehyde, formic acid, formate, dioxymethylene and polyoxymethylene surface species are formed during formaldehyde adsorption at 300-473 K. The main gas phase products were H-2 and CO; their amounts increased with the increase of the metal content of the catalysts and with the increase of the reaction temperature. Gas phase ethylene, acetylene, as well as formic acid were detected on pure TiO2. On metal-containing TiO2 no ethylene, acetylene and formic acid were observed, which could be connected with the limited surface concentration of oxygen vacancies on these surfaces. (C) 2004 Elsevier B.V. All rights reserved.