Catalytic performance of titania supported nickel catalyst (Ni/TiO2) with pre-treatments for the selective methanation of CO (CO-SMET) in reformate gas has been studied to elucidate the role of chlorine component in the methanation activity and CO/CO2 reaction selectivity in CO-SMET. Raw commercial TiO2, used as the support material, contains a certain amount of chlorine component, and the chlorine component can be removed by the heat treatment in air and water washing treatment. The Ni/TiO2 catalyst prepared from the TiO2 containing chlorine component exhibited high CO/CO2 reaction selectivity, that is, low CO2 methanation activity due to its low reverse water gas shift (r-WGS) activity, while the catalysts containing no chlorine component displayed quite low selectivity. The evaluation of the activity of the Ni/TiO2 catalysts prepared from the starting Ni salts with different mixing molar ratios of Ni chloride and Ni nitrate indicates that a trace amount of chlorine led to the improved CO/CO2 reaction selectivity in CO-SMET. The chlorine component in the Ni/TiO2 catalysts is considered to be located on the interface of the Ni particles and the TiO2 support, giving rise to the suppression of CO2 methanation via the r-WGS step. (C) 2015 Elsevier B.V. All rights reserved.