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Catalytic Decomposition Kinetics of Aqueous Hydrogen Peroxide and Solid Magnesium Peroxide By Birnessite
Author(s) -
Elprince A. M.,
Mohamed W. H.
Publication year - 1992
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1992.03615995005600060021x
Subject(s) - birnessite , chemistry , catalysis , hydrogen peroxide , aqueous solution , decomposition , inorganic chemistry , reaction rate constant , activation energy , ionic strength , magnesium , diffusion , ionic bonding , kinetics , ion , thermodynamics , organic chemistry , manganese oxide , physics , quantum mechanics
Peroxides are used as O 2 ‐generating agents. The decomposition of H 2 O 2 (aq) or MgO 2 (s) in the presence of synthetic birnessite [δ‐MnO 2 (s)] as a catalyst was observed by measuring the volume of O 2 (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 H 2 O 2 (aq). The applicability of the proposed mechanism involving H 2 O 2 (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 Mn z+1 /Mn z active centers. Regarding MgO 2 (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, MgO 2 (s) could be a potential O 2 ‐generating agent for generating O 2 (g) during a relatively long period of time.