ACTIVITY OF SILICA-ALUMINA SURFACE-MODIFIED WITH SOME TRANSITION-METAL IONS

Kinetics of H2O2 decomposition have been investigated in the presence of a silica-alumina surface (25% Al2O3) modified with transition metal ions including Cu(II), Co(II), and Fe(III). The decomposition reactio n proceeded with first-order kinetics with respect to the peroxide con centration. The rate of reaction depends upon the type of ions. The re action rate and the energy of activation decrease in the order Cu(II) > Co(II) > Fe(III). The initial concentration of H2O2 has a great infl uence on the reaction rate and the coloration of the surface. The deco mposition reaction involved the generation of free radical species as confirmed by using the reference chromogen 2,2'-azino-bis(3-ethylbenzt hiazoline)-6-sulphonate diammonium salt asa probe. An isokinetic relat ionship indicates that the reaction is entropy-controlled. A probable mechanism has been suggested for the decomposition process which agree s with the results obtained.