The promoting effect of Co addition on the behaviour of the Pd/HAP system in WGS reaction has been investigated. Hydroxyapatite-supported bimetallic Pd-Co samples have been prepared by two consecutive impregnation steps with solutions of Co and Pd precursors, respectively. The resulting catalysts have been thoroughly characterised by BET, XRD, H-2-TPR, XPS, OSCC and OSC techniques. The progressive addition of cobalt drives to an abundance of the Pd species exhibiting an intimate contact with Co and an eminent enhancement of the redox properties of the Pd/Co(x)/HAP catalysts. This results in an improvement of their performance in WGS reaction. The 'Pd species presenting an intimate contact with cobalt seems to be the responsible of the improvement of the CO conversion. However, this Pd Co interaction leads to an increase in the methanation activity at the expense of WGS activity. When small amounts of 02 is added to the WGS mixture, the activity is exclusively enhanced in the presence of Co species exhibiting easier reducibility. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.