Kinetics and mechanism of H2O2 decomposition by Cu(II)-, Co(II)-, and Fe(III)-Amine complexes on the surface of Silica-Alumina (25% Al2O3)

Abstract

The kinetics of the H2O2 decomposition by Cu(II)-, Co(II)-, and Fe(III)-amine complexes supported on the surface of silica-alumina (25% Al2O3) catalyst have been investigated. The decomposition process proceeded with first-order kinetics for the substrate concentration. With copper complexes, in particular, the rate of reaction decreased in the sequence: ethylenediamine (en) > monoethanolamine (mea) > triethanolamine (tea). With ethylenediamine as aligand, the rate has also decreased in the order: Cu(II) > Co(II) > Fe(III). Both of the energy and entropy of activation were found to decrease as: en > mea > tea and for one ligand (en) and different metal ions the sequence was Cu(II) > Co(II) > Fe(III). The decomposition reaction involved the formation of an intermediate active species, which converts into a peroxo-metal-complex of brown or faint red color. The rate of reaction was directly proportional to the [complex], [H2O2], and [H]?1. A mechanism describing the decomposition process is proposed.