The influence of the addition of the reaction products (CO2 and H-2) to the feed during the partial oxidation of methanol (POMeOH) was studied over a Cu/ZnO/gamma-Al2O3 catalyst. The addition of the reaction products influences in a significantly way the selectivity to hydrogen during the reaction. The observed changes are not due to the changes suggested by the thermodynamics when promoter gases are added and might be interpreted by considering modifications in the physicochemical properties of the catalysts, particularly in the kinetic of the reactions involved in POMeOH process. In some cases CO-free hydrogen (namely highly pure, CO is not observed in analysis) could be obtained by POMeOH. The processes consider the modulation of the selectivity by a controlled amount of CO2 and/or H-2 into the reaction flux. The presence of promoter gases strongly influenced the Cu oxidation state. It is concluded that the inhibition in CO formation is related to the high content of Cu-0. It is suggested that in the presence of metallic copper the kinetic of the several reactions involved during POMeOH, facilitates the formation of H-2 and CO2 and inhibits the CO formation. Results are useful for processes where the CO/H-2 ratio has to be reduced drastically (fuel cells)lor finely modulated (Fischer Tropsch, methanol synthesis, etc.). (C) 2014 Elsevier B.V. All rights reserved.