Heterogeneous kinetic studies of the hydrogen peroxide decomposition with some transition metal-heterocyclic complexes

The heterocyclic compounds piperidine (Pip), piperazine (Pz), morpholine (Morph), and N-methyl piperazine (N-MPz) were used as ligands to form transition metal complexes with Ni(II), Cu(II), and Co(II) ions. These complexes were supported on Dowex-50W resin so as to form new potential active catalysts for H₂O₂ decomposition in an aqueous medium. In all cases the reaction showed a first-order kinetics with respect to H₂O₂ concentration, except with Co(II) complexes, the reaction showed a second-order kinetics with 2% divinyl benzen (DVB) (50-100 mesh and 200-400 mesh). The rate constant k (per gram dry resin) was evaluated with a resin of cross-linkage 2 and 8% DVB (50-100 mesh) and 2% DVB (200-400 mesh) over temperature range 25-40°C. With a given resin cross-linkage, the rate constant has the following order: Ni(II) complexes < Co(II) complexes < Cu(II) complexes. With Pz ligand, k increased in the following sequence: Ni(II) complexes < Cu(II) complexes < Co(II) complexes. The reaction mechanisms of the first- and second-order kinetics were discussed and the activation parameters were deduced.