The decomposition of formic acid on Rh/TiO2 and Au/TiO2 catalysts was examined at 300-473 K with Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS). Besides molecularly adsorbed HCOOH and formate species (produced in the HCOOH dissociation on the surfaces), formation of formaldehyde was detected by FTIR in the adsorbed layer. The surface concentration of formaldehyde depended on the nature of the metal, as well as on the reaction temperature. A part of formaldehyde desorbed from the adsorbed layer, another part, however. decomposed into H, and CO. It is suggested that CO is not the product of the direct dehydration of HCOOH. CO is rather produced in the decomposition of formaldehyde originating from the deoxygenation of HCOOH. (C) 2004 Elsevier B.V. All rights reserved.