LaNiO3 perovskite has been successfully used as a catalyst precursor for high temperature water -gas shift (HT-WGS) reaction of reformate gas to produce additional hydrogen from the hydrocarbon reforming. The Ni-0 nanoparticles with the particle size of ca. 21 nm obtained after reduction of LaNiO3 perovskite can effectively suppress CO methanation during HT-WGS reaction using pure CO/H2O gas. However, for HT-WGS reaction of reformate gas (including CO, H2O, CO2 and H-2), LaNiO3 perovskite exhibits lower catalytic activity with significant CH4 formation predominantly via CO2 methanation. In this work, the CO2 methanation during HT-WGS reaction of reformate gas was suppressed by the addition of (p)otassium onto LaNiO3 perovskite. This is due to the adsorption of H2O on the potassium which is located at the interface between La2O3 and Ni nanoparticle (as deduced from XPS and HRTEM results) that forms stable K OH, blocking the methanation of CO2 adsorbed on the La2O3 with H-2 adsorbed on the Ni nanoparticles. Moreover, the formation of stable K OH also promotes the formation of formate (HCOO) a key intermediate for WGS reaction over the reduced LaNiO3 perovskite even at high reaction temperature by continuously supplying hydroxyl group to react with CO adsorbed on the Ni nanoparticle, which helps to maintain the catalytic activity for WGS reaction at high reaction temperature. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.