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the oxidation of NH3 to hydroxylamine

This research describes the heterogeneous catalytic reactions of H2O2 with granular size goethite (α-FeOOH) particles in aqueous solution under various experimental conditions. This is an important reaction for the environment since both H2O2 and iron oxides are common constituents of natural and atmospheric waters. Furthermore, iron oxides function as catalysts in chemical oxidation processes used for treatment of contaminated waters with H2O2. The results of this study demonstrated that the decomposition rate of H2O2 over goethite surface can be described by the second-order kinetic expression −d[H2O2]/dt = k[FeOOH][H2O2], where k = 0.031 M1 s1, at pH 7 in the absence of any inorganic or organic chemical species. The apparent reaction rate was dominated by the intrinsic reaction rates on the oxide surfaces rather than the mass transfer rate of H2O2 to the surface. The activation energy of the reaction of H2O2 with the iron oxide surface was determined to be 32.8 kJ/M. The reaction mechanism for the decomposition of H2O2 on goethite surface was proposed on the basis of the fundamental reactions describing the surface complexation chemistry for iron oxide and the interaction of H2O2 with the surface sites. The kinetic model, which was developed according to the proposed mechanism, was found to be similar to the classical Langmuir−Hinshelwood rate model. The model was calibrated and verified successfully. For low concentrations of H2O2, the Langmuir−Hinshelwood model is reduced to the observed second-order kinetic expression.