Various Co3O4 catalysts were investigated for the water gas shift (WGS) reaction for hydrogen production. Although the catalyst supporting only palladium (Pd/Co3O4) showed low catalytic activity and higher selectivity to methanation, Pd/K/Co3O4 catalyst, with loading of potassium exceeding 0.78 wt%, showed high catalytic activity for the WGS reaction. Catalysts on which Pd and K exist closely showed high activity, as confirmed using various preparation methods. Results of XPS measurements for Pd/K/Co3O4 revealed that supported potassium donated electrons to Pd and Co. The state of CO adsorption species was affected by the potassium loading, resulting in high catalytic activity for the Pd/K/Co3O4 catalyst. These effects gave the Pd/K/Co3O4 catalyst high catalytic activity for the WGS reaction. That reaction over Pd/K/Co3O4 proceeds via surface cobalt carbonyl and then formate intermediates, as revealed by the TG and isotope exchange measurements using (H2O)-O-18 and DRIFT. (C) 2014 Elsevier B.V. All rights reserved.