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

Abstract

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 N20. 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 N H4NO2 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⁺.