Abstract Optimum operating conditions are established for the regeneration of the deactivated Midrex reformer nickel-alumina (Ni/Al2O3) catalysts employed in Khouzestan Steel Company (KSC) using supercritical carbon dioxide. In addition, the impacts of a range of parameters, including static time, flow rate, pressure, and temperature, on extraction efficiency of the deactivated materials from the catalyst are elucidated through sensitivity analysis. The results show that the optimum regeneration conditions of the Midrex reformer unit catalysts are at a pressure of 180 bar, static time of 90 min and flow rate of 0.5 cm3/s, or less. SEM (scanning electron microscope) analysis reveals that the presence of sulfur compounds and coke are the main factors leading to the deactivation of the catalysts. Moreover, crushing strength, XRD (X-ray Diffraction), XRF (X-ray fluorescence), CHNSO (Carbon, Hydrogen, Nitrogen, Sulfur, and Oxygen), SEM analyses and nickel content confirm that the composition of the regenerated catalysts is substantially improved and restored in comparison with the deactivated catalysts.