A comparative study has been performed to investigate the effectiveness of a Ni metal catalyst before and after impregnation with potassium for the water-gas shift (WGS) reaction. The potassium-modified Ni metal is both more active and more selective for the WGS reaction than the unmodified Ni catalyst. Furthermore, there is no carbon deposition on the modified Ni catalyst. The amount of H-2 produced and the CO conversion via WGS over the potassium-modified Ni catalyst are higher than those for the commercial high-temperature shift (HTS) catalyst under severe experimental conditions (gas-hourly space velocity = 80000 h(-1), CO 60% and H-2 40%). The suppression of methanation over the modified Ni metal is attributed to the action of the incorporated potassium in increasing the density of the active hydroxyl group that takes part in the WGS reaction to form the intermediate. (C) 2010 Elsevier B.V. All rights reserved.