Catalytic wet oxidation of ammonia:: Why is N2 formed preferentially against NO-3?

The role of catalyst and the reason for the preferential formation of N-2 in the catalytic oxidation reaction of ammonia in water over a Ru (3 wt.%)/TiO2 catalyst were elucidated. It was verified that the catalyst in the reaction had no direct relevance to the selective formation of N-2, but was responsible only for the oxidation of aqueous ammonia, NH3(aq), finally giving a molecule of nitrous acid. The preferential production of N-2 was experimentally demonstrated due to the homogeneous aqueous phase reaction of the nitrous acid-dissociated NO2- with NH4+ ions. Even under the highly oxidizing condition, NO2- was much more likely to react with NH4+ to form N-2 than being oxidized over the catalyst to NO3- as long as NH4+ was available in solution. (C) 2005 Elsevier Ltd. All rights reserved.