In this work the methane steam reforming (MSR) and the ethanol steam reforming (ESR) on Ni(II)-Al(III) catalyst prepared from lamellar double hydroxides (LDHs) as precursor are studied. A comprehensive analysis of the kinetics results obtained at different water/methane and water/ethanol feed ratio and its correlation with the structural characteristic and redox behavior of the catalyst is carried out. The results show evidence that the catalyst behavior is related with the presence of only one type of active site in the Ni/Al2O3 catalyst. The competition for the active sites between reactants is verified for MSR. This behavior is also observed in ethanol steam reforming since methane steam reforming determines the products distribution in the exit stream. There would be an optimum inlet water concentration that gives a maximum performance in terms of H, and CO, selectivity and, simultaneously, a minimum CO selectivity. This is a promissory result taking into account that the hydrogen flow entering a PEM fuel-cell requires a CO concentration lower than 20 ppm. (c) 2006 Elsevier B.V. All rights reserved.