Minimum-energy pathways for the demethanation reaction CH3OH + Ni-n(+) (n = 3,4)-> NinO(+) + CH4 have been computed to examine why this reaction occurs preferentially on Ni-4(+). Stationary points of paths for the demethanation of CH3OH on Ni-n(+) (n = 3,4), which provide possible reaction pathways, were characterized and the associated activation barriers were evaluated on both Ni-3(+) and Ni-4(+) via density-functional theory calculations. On Ni-4(+), all the transition states along the minimum-energy path are energetically below the reactant asymptote, whereas on Ni-3(+), the transition states are above it. (C) 2011 Elsevier B. V. All rights reserved.