The effect of nitrogen content in N-doped carbon nanofibers (N-CNFs) on the catalytic activity of Ru/N-CNFs in the wet air oxidation of phenol has been studied. The N-CNFs, irrespective of nitrogen content and Sibunit, are shown to be low active. In the case of Ru-containing catalysts, nitrogen in N-CNFs was found to be responsible for both the increased activity and stability of the catalysts toward deactivation. The XPS showed the formation of carbon-oxygen structures with hydroxyl (carbonyl) end groups blocking ruthenium on the surface of the catalysts without nitrogen. For the catalysts with nitrogen, the ruthenium nanoparticles were not blocked in the course of the reaction and mainly the carboxyl (carbonate) surface groups were formed. The nature of this effect is discussed. (C) 2013 Elsevier B.V. All rights reserved.