Catalytic Decomposition of Hydrogen Peroxide by Fe(III) in Homogeneous Aqueous Solution: Mechanism and Kinetic Modeling

Abstract

This paper describes a kinetic model for the decomposition of hydrogen peroxide by ferric ion in homogeneous aqueous solution (pH < 3). The reaction was investigated experimentally at 25.0 °C and I = 0.1 M (HClO4/NaClO4), in a completely mixed batch reactor and under a wide range of experimental conditions (1 ≤ pH ≤ 3; 0.2 mM ≤ [H2O2]0 ≤ 1 M; 50 μM ≤ [Fe(III)]0 ≤ 1 mM; 1 ≤ [H2O2]0/[Fe(III)]0 ≤ 5000). The results of this study demonstrated that the rate of decomposition of hydrogen peroxide by Fe(III) could be predicted very accurately by a kinetic model which takes into account the rapid formation and the slower decomposition of Fe(III)−hydroperoxy complexes (FeIII(HO2)2+ and FeIII(OH)(HO2)+). The rate constant for the unimolecular decomposition of the Fe(III)−hydroperoxy complexes was determined to be 2.7 × 10-3 s-1. The use of the kinetic model allows a better understanding of the effects of operational parameters (i.e., pH and [H2O2]0/[Fe(III)]0) on the complex kinetics of decomposition of H2O2 by Fe(III).