Oxidation of Dilute Ammonium Ion in Aqueous Phase Catalyzed
by RuO2 Supported on Al2O3 under Pressure of Air

Hiromu HAYASHI*, Masahiro UNO, Michiya CHIYO and Shigeru SUGIYAMA

Department of Chemical Science and Technology, Faculty of Engineering, University of Tokushima;
2-1, Minamijosanjima, Tokushima-shi 770-8506 Japan

The oxidation of dilute ammonium ion (1500 ppm NH4+) catalyzed by RuO2 supported on Al2O3 was carried out at 140--220 °C in an aqueous suspension phase under pressure of air, as a model for waste water treatment. Helium-diluted oxygen (19.3% O2/He) was used as an oxidant to be capable of analyzing product N2. 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 °C, but resulted in an increase in the unfavorable by-product NO3 above 220 °C. Besides the oxidation of NH4+, molecular nitrogen was also produced through decomposition of NH4NO2 without catalyst and oxygen at lower temperature of 120--160 °C. The amounts of oxygen and nitrogen contained in the products were well corresponding to the observed consumptions for oxygen and NH4+.

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