Density functional theory (DFT) calculations have been carried out to investigate the structural sensitivity of the elementary processes in CO methanation at low coverage of 0.25 ML, including CO dissociation via either direct or H-assisted path and CHx (x = 0-3) hydrogenation, on Co (0 0 0 1), (1 0(-)1 2) and (1 1(-)2 0) surfaces. CO direct dissociation was found to be structurally most sensitive, whereas CHx hydrogenation is structurally least sensitive. Specifically, the barrier of CO direct dissociation, H-assisted dissociation and CHx hydrogenation on different surfaces varies in range of 1.12, 0.54 and 0.34 eV, respectively. Regardless of Co surfaces considered, the CO activation is the rate-limiting step of methanation reactions, which would proceed through the H-assisted pathway on Co (0 0 0 1), whereas through both direct and H-assisted pathways on more active Co (1 0(-)1 2) and (1 1(-)2 0) surfaces. The structure sensitivity of CO activation leads to methanation reaction structural sensitive. (C) 2013 Elsevier B.V. All rights reserved.