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The potassium promotion to nickel catalysts has been described to suppress the activity of CO hydrogenation to CH4. In this work, Ni/MgAl2O4 promoted with potassium is applied in steam reforming (SR) of organic molecules. The ethanol (EtOH), Butanol (ButOH) and phenol (PhOH) were used as model molecules with the expectation of generating different CHX groups on Ni surface and analyze the effect of potassium on suppression of the methane formation in SR of compounds with different structures. The catalysts were characterized by nitrogen adsorption, in situ XRD TPR-H2, TEM and X-ray absorption spectroscopy (XANES). The catalytic tests of PhOH and EtOH were performed between 250/300°C-600/650°C, using about 13 steam/carbon molar ratio. The K addition to Ni catalysts seems to weaken the NiO - support interaction, causing NiO agglomeration and bigger particles as observed by XRD, TPR and XANES analysis. The effect of K on suppression of CH4 formation is strongly dependent on structures organic compounds, being highly efficient on suppressing hydrogenation to CH4 when an aromatic is used, whereas in linear compounds such as ethanol the effect of K is modest.