A comparative study of the GSR performance for Ni/CaO-MgO-Al₂O₃ and Ni/Al₂O₃ catalysts is reported. Catalysts were synthesized applying the wet impregnation method at a constant metal loading (8 wt %). Synthesized samples were characterized by N₂ adsorption/desorption, ICP, BET, XRD, NH₃-TPD, CO₂-TPD, H₂-TPR, XPS, TEM, STEM-HAADF and EDS. The carbon deposited on their surface under reaction conditions was characterized by TPO, Raman and TEM. It was proven that the use of CaO-MgO as alumina modifiers leads to smaller nickel species crystallite size, increased basicity and surface amount of Ni⁰ phase. Thus, it increases the conversion to gaseous products favoring H₂ and CO₂ production to the detriment of CO formation, by enhancing the water gas-shift (WGS) reaction. No liquid products were produced by the Ni/modAl catalyst over 550 °C, whereas time on stream results confirmed that deactivation can be prevented, as apart from decreasing the amount of coke deposition the nature of carbon was altered towards less graphitic and more defective structures.