A dual-site reaction mechanism is proposed for Pt based water-gas shift catalysts. The sorption equilibrium parameters are evaluated in detail to validate their physical significance. The values of the van 't Hoff parameters for CO and H 2 correspond to those for chemisorption on platinum. The sorption parameters of H 2 O and CO 2 on the supports have been quantitatively determined from temperature-programmed desorption experiments and have been compared to the values obtained from the kinetic study. Finally the proposed model is able to explain the different activities between the two catalysts.Keywords WGS Á Temperature-programmed desorption Á Dual-site Á CeO 2 Á TiO 2 Á Water adsorption List of symbols e bReactor void space m 3 gas m À3 reactor C i Gas phase concentration of species i mol m À3 gas h i Surface coverage of species i (-) D ax,i Axial diffusion coefficient m 3 gas m À1 reactor s À1

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