Catalytic Decomposition Kinetics of Aqueous Hydrogen Peroxide and Solid Magnesium Peroxide By Birnessite

Abstract

AbstractPeroxides are used as O2‐generating agents. The decomposition of H2O2 (aq) or MgO2(s) in the presence of synthetic birnessite [δ‐MnO2(s)] as a catalyst was observed by measuring the volume of O2(g) given off. The experimental data fit a first‐order kinetic law and the mechanism proposed by Habes and Weiss can explain the experimental results obtained for the decomposition of H2O2(aq). The applicability of the proposed mechanism involving H2O2(aq) was based on the following: (i) the activation energy was relatively high (82 ± 3 kJ mol−1); (ii) the rate constant (k) was pH dependent, indicating that H+ and OH‐ ions were formed in the process; (iii) a linear relationship (and not logarithmic) between k and the ionic strength indicated a reaction between an ion and a neutral molecule; and (iv) using birnessite with different fractional coverages of Co indicated that the reaction was heterogeneously catalyzed by Mnz+1/Mnz active centers. Regarding MgO2(s) decomposition, the experimental data obtained at pH 7.6 followed a rate law derived from a shrinking‐core model for fixed‐size particles. The rate of the reaction was controlled by diffusion through the Mg(OH)2(s) product layer rather than by chemical reaction at the core surface. Compared with ionic peroxides, MgO2(s) could be a potential O2‐generating agent for generating O2(g) during a relatively long period of time.