Hydrogen peroxide decomposition in ammonia solutions

The decomposition of H2O2 in ammonia hydroxide peroxide mixtures (BPM) have been studied as a function of metal-ion weight concentration (0.1-10 ppb r ange) and temperature. It has been found that the uncatalyzed self-decompos ition of H2O2 is second order with an activation energy of 170 (+/- 10) kJ/ mol. Additionally, copper ions, which form mononuclear ammonia complexes ca talyze the H2O2 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 m ixture of first and second order. Due to the insolubility of Fe(III) it agg regates to large clusters or colloid particles. Higher concentrations of th e large clusters shift the reaction kinetics from first order to second ord er The first and second order iron-ion catalysed decomposition reactions ha ve similar activation energies [65 (+/-4) and 71 (+/-4) kJ/mol] suggesting a similar primary reaction step. Furthermore, the effect of complexing agen ts has been evaluated. Substoichiometric amounts of diethylenetriamine-NNN' N"N"-penta(methyphosphonic) acid break down these iron clusters favoring th e first order reaction at the expense of the second order reaction. Superst oichiometric amounts of the complexing agent completely inactivate the iron ions, but had no effect on the copper-ion catalyzed decomposition reaction . (C) 1999 The Electrochemical Society. S0013-4651(98)10-090-3. All rights reserved.