In this study, strong basic sites were introduced into Ni/Al2O3 catalysts via modification of the catalysts with the strong base like KOH. Effects of the basic sties on physiochemical properties of the catalysts and the reaction intermediates formed in methanation and reverse water gas shift reaction (RWGS) were investigated. The KOH added to the catalyst reacted with alumina, leading to the collapse of the porous structure, the decreased surface area and the aggregation of metallic nickel. The addition of KOH also introduced abundant weak, medium and strong basic sites, which helped to absorb/activate CO2 and further converted CO2 to CO through RWGS reaction via a formate intermediate formed. In the absence of KOH, carbonates were the main intermediates, decomposition of which to CO was relatively difficult. The in-situ DRIFTS study showed that the formate intermediates strongly absorbed on surface of Ni-KOH/Al2O3 catalyst, preventing the further hydrogenation of CO intermediates to CH4. However, the catalyst had high activity for the RWGS reaction to form CO. CO is a major byproduct in steam reforming reactions. The superior activity of Ni-KOH/Al2O3 for RWGS reaction contributed to CO formation when the catalyst was applied in steam reforming reactions.