Dissociation of methane on Ni4 cluster-A DFT study

The sequential four step dissociation of methane on Ni-4 cluster has been investigated using density functional theory. The adsorption of CH4, CHx, C and H are exothermic and Gibbs free energy changes are negative on bare cluster. The dissociation of methane on Ni4 cluster is endothermic and thermodynamically not favorable at standard condition (T = 298 K, P = 1 atm). The dissociation of CHx (x = 1-3) species on bare cluster show higher activation energy barrier than on the hydrogen preadsorbed cluster. The elementary step, CH -> C, shows the highest activation energy barrier. Hence CH is the most stable intermediate. The Gibbs free energy changes are negative above 450 K for CH4 CH3, CH3 CH2 and CH2 CH, whereas for CH -> C above 550 K at 1 atm. Coke formation is possible above 550 K. (C) 2017 Elsevier By. All rights reserved.