The influence of metal (Pt, Ni) loading and the nature of the active surface of carbon-supported metal catalysts on the reaction of ammonia oxidation have been investigated to understand the high N-2 selectivity of some catalysts. The comparison of the activities of catalysts has shown that NH3 is converted into N-2, N2O and NO. For all examined catalysts, the N-2 selectivity depends on the temperature of the reaction. Parallel in situ investigations reveal the presence of intermediate surface species. The NH3 chemisorption on the oxidized carbon sample leads to the formation of the bands attributed to ammonium salts of carboxylic acids. Their rearrangement causes the formation of amide and imide structures. With the rise of the reaction temperature the bands, attributed to -CN at 2158 cm(-1) and -NCO at 2220 cm(-1) appear. (C) 2002 Elsevier Science B.V. All rights reserved.