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(lf), 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 benzene (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 degreesC. 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(Il) complexes < Co(II) complexes, The reaction mechanisms of the fist- and second-order kinetics were discussed and the activation parameters were deduced. <(c)> 2001 John Wiley & Sons, Inc.