The mechanism of the liquid phase methanol reforming reaction over silica supported Pt-Ru catalyst was investigated by kinetic studies, employing a pyrex glass reactor with reflux condensers connected to a closed gas circulation system under ambient pressure. The rate of H-2 formation over Pt-Ru/SiO2 catalysts was more than 20 times faster than that over Pt/SiO2 catalysts with high selectivity for CO2 (72.3%), indicating a marked addition effect of Ru. In the case of HCHO-H2O reaction over Pt-Ru/SiO2, the H-2 formation rate was five times larger than that in the CH3OH-H2O reaction but selectivity to CO2 was only 4%. On the contrary, in the HCOOCH3-H2O and HCOOH-H2O reactions, both high activity and selectivity were observed over Pt-Ru/SiO2. These results clearly indicate that the CO2 formation does not proceed via HCHO decomposition and following water gas shift reaction. We propose the following pathway for liquid phase methanol reforming reaction over Pt-Ru/SiO2; a partly dehydrogenated methanol (CH2OH*) is the initial reaction intermediate, from which H-2 and CO2 are formed through HCOOCH3 and HCOOH as the successive reaction intermediates. (C) 2003 Elsevier B.V. All rights reserved.