The wet H-2-rich gas was used as reducing gas instead of the H-2/N-2 gas in the reduction step of the catalyst preparation. It is found that the selectivity for CO methanation over the catalysts 0.4Ni/ZrO2 so-obtained was decreased in comparison to the case of the H-2/N-2 gas used as reducing gas. Even though, the samples with the different feed atomic ratios of Ni/Zr prepared by the impregnation method and the co-precipitation method, respectively, were evaluated with the wet H-2-rich gas both as reducing gas and as reactant gas. The catalysts Ni/ZrO2-CP prepared by the co-precipitation method exhibited a high catalytic activity for CO removal at a lowered reaction temperature with increasing the Ni loading. Over the catalyst 3.0Ni/ZrO2-CP, CO in the reactant gas could be removed to below 10 ppm at reaction temperatures of 220-260 degrees C with the selectivity higher than 50%. And the selectivity was kept at 100% during the 100 h test at 220 degrees C. The catalysts were characterized by XRD, XPS, XRF and the adsorption isotherm measurement. In addition, effect of water vapor in reactant gas was studied over the catalysts 0.4Ni/ZrO2 with the wet H-2-rich gas and the dry H-2-rich gas as reactant gas, respectively, in the case of the H-2/N-2 gas fixed as reducing gas. It is seen that presence of water vapor in the reactant gas retarded methanation reactions of CO and CO2 on the catalysts. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.