Oxidation of dilute ammonium ion in aqueous phase catalyzed by RuO2 supported on Al2O3 under pressure of air

The oxidation of dilute ammonium ion (1500 ppm NH4+) catalyzed by RuO2 supported on Al2O3 was carried out at 140-220 degrees C in an aqueous suspension phase under pressure of air, as a model for waste water treatment. Helium-diluted oxygen (19.3% O-2/He) was used as an oxidant to be capable of analyzing product N-2. Molecular nitrogen was the predominant product with NO2- followed by the subsequent oxidation to give NO3- with a small amount of by-product of N2O. The catalyst activity in oxidation of NH4+ was strongly dependent on pH values, and the reaction was not observed in acidic condition, while NH4+ was quickly oxidized in basic region. The oxidation of NH4+ should be carried out at high temperature around 200 degrees C, but resulted in an increase in the unfavorable by-product NO3- above 220 degrees C. Besides the oxidation of NH4+, molecular nitrogen was also produced through decomposition of NH4 NO2 without catalyst and oxygen at lower temperature of 120-160 degrees C. The amounts of oxygen and nitrogen contained in the products were well corresponding to the observed consumptions for oxygen and NH4+.