Spin-polarised density functional theory using the PBE + U approach are used to determine reaction pathways of successive NH3 dehydrogenation on the CoO(100) surface. NH3 dehydrogenation promotes noticeable displacements of the surface CoO sites, in particular due to the binding of NH2 and H species. Surface lattice O has low activity towards dehydrogenation, reflected in energy barriers that are in the range of 292 kJ mol(-1) to 328 kJ mol(-1). There is a preference of surface NH3 dehydrogenation to N-2 rather than towards NO, due to a high-energy penalty of surface O vacancy formation. The presence of CoO in cobalt oxide catalysts not only may decline the ammonia conversion but also alter the selectivity towards Ny rather than NO. (C) 2015 Elsevier B.V. All rights reserved.