Kinetics of Nonenzymatic Decomposition of Hydrogen Peroxide by Torrifluvents

Peroxide application has been proposed as a method to control soil aeration. The objectives of this study were to formulate the rate law, identify the inorganic catalyst, identify preferred active centers, and hypothesize a mechanism for the H 2 O 2 decomposition reaction in Torrifluvents. The rate of decomposition of H 2 O 2 (aq) by Torrifluvents (10 locations in the Nile Delta) and synthetic Mn oxides was determined by measuring with a gas burette the volume of O 2 (g) given off. Heat pretreatment showed that the catalytic activity of the air‐dried soil is essentially nonenzymatic on the time scale of the reaction. Pretreatment of the soil samples by NH 2 OH–HCl (pH 2), designed for selectively dissolving MnO 2 (s), completely deactivated their catalytic capacity. The pseudo‐first‐order rate coefficient, k *, for Torrifluvents was expressed by the equation: k * = k o [MnO 2 (s)](10 −pH/4 ), where k o is a constant. Contrary to cryptomelane and pyrolusite, values of k * for birnessite satisfied the above equation, indicating that pedogenic birnessite was the active catalyst in Torrifluvents. Diethylenetriamine pentaacetic acid (DTPA) was found to be a more effective inhibitor than ethylenediamine tetraacetic acid (EDTA). A high value of the activation energy ( E ) was connected with a high value of the pre‐exponential factor ( A ) of the Arrhenius equation. It was suggested that the birnessite surface has two kinds of active centers: Mn III /Mn II and Mn IV /Mn III While the former is less numerous (ln A = 37 ± 4) with low activation energy ( E = 75 ± 4 kJ mol −1 ), the latter is numerous (ln A = 62 ± 3) and of high activation energy ( E = 144 ± 17 kJ mol −1 ). The Habes and Weiss mechanism explained the experimental results obtained.