Catalytic Decomposition of Hydrogen Peroxide on Iron Oxide: Kinetics, Mechanism, and Implications

Abstract

This research describes the heterogeneous catalytic reactions of H 2 O 2 with granular size goethite (α-FeOOH) particles in aqueous solution under various experimental conditions. This is an important reaction for the environment since both H 2 O 2 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 H 2 O 2 . The results of this study demonstrated that the decomposition rate of H 2 O 2 over goethite surface can be described by the second-order kinetic expression −d[H 2 O 2 ]/d t = k [FeOOH][H 2 O 2 ], where k = 0.031 M - 1 s - 1, 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 H 2 O 2 to the surface. The activation energy of the reaction of H 2 O 2 with the iron oxide surface was determined to be 32.8 kJ/M. The reaction mechanism for the decomposition of H 2 O 2 on goethite surface was proposed on the basis of the fundamental reactions describing the surface complexation chemistry for iron oxide and the interaction of H 2 O 2 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 H 2 O 2, the Langmuir−Hinshelwood model is reduced to the observed second-order kinetic expression.