Hydrogen Peroxide Decomposition in Ammonia Solutions

Abstract

The decomposition of in ammonia hydroxide peroxide mixtures (APM) have been studied as a function of metal‐ion weight concentration (0.1‐10 ppb range) and temperature. It has been found that the uncatalyzed self‐decomposition of is second order with an activation energy of 170 (±10) kJ/mol. Additionally, copper ions, which form mononuclear ammonia complexes catalyze the decomposition. Superimposed on the uncatalyzed reaction, a first order copper‐ion catalyzed decomposition with an activation energy of 84 (±2) kJ/mol has been measured. The iron‐ion catalyzed reaction is a mixture of first and second order. Due to the insolubility of Fe(III) it aggregates to large clusters or colloid particles. Higher concentrations of the large clusters shift the reaction kinetics from first order to second order. The first and second order iron‐ion catalyzed decomposition reactions have similar activation energies [65 (±4) and 71 (±4) kJ/mol] suggesting a similar primary reaction step. Furthermore, the effect of complexing agents has been evaluated. Substoichiometric amounts of diethylenetriamine‐NNN′N″N″‐penta(methylphosphonic) acid break down these iron clusters favoring the first order reaction at the expense of the second order reaction. Superstoichiometric amounts of the complexing agent completely inactivate the iron ions, but had no effect on the copper‐ion catalyzed decomposition reaction. © 1999 The Electrochemical Society. All rights reserved.