It is attempted to optimize preparation of ZrO2 as support of the nickel catalysts for selective methanation of CO in H-2-rich gas (CO-SMET). Therefore, the supports ZrO2 were prepared at first by thermal decomposition method from zirconium oxynitrate and zirconium oxychloride at the calcination temperature of 400 degrees C and 800 degrees C, respectively. It is illustrated that the salt kind and calcination temperature affected phase state (tetragonal, monoclinic), crystallite size and specific surface area (SSA) of the supports. The difference in property of the supports influenced catalytic performance of the catalysts Ni/ZrO2 for CO-SMET reaction. Especially, the chlorine ion residues in the support ZrO2 prepared from zirconium oxychloride was beneficial for CO removal selectively. Furthermore, a precipitation method was adopted to prepare ZrO2 for comparison with the thermal decomposition method with use of the zirconium oxychloride as starting material. It is found that the supports ZrO2 prepared by the precipitation method induced a better dispersion of metallic Ni on its surface. The catalyst Ni/ZrO2 with use of the support ZrO2 prepared by the precipitation method and calcination at 400 degrees C exhibited a good performance at the reaction temperature of 220 degrees C in the 100 h durability test, where CO outlet concentration was kept below 10 ppm and the selectivity remained constant at 100%. Relation of Ni crystallite size and chlorine ion residues with the catalytic performance was discussed. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.