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 reaction proceeded with first-order kinetics with respect to the peroxide concentration. The rate of reaction depends upon the type of ions. The reaction rate and the energy of activation decrease in the order Cu(II) > Co(II) > Fe(III). The initial concentration of H2O2 has a great influence on the reaction rate and the coloration of the surface. The decomposition reaction involved the generation of free radical species as confirmed by using the reference chromogen 2,2'-azino-bis(3-ethylbenzthiazoline)-6-sulphonate diammonium salt asa probe. An isokinetic relationship indicates that the reaction is entropy-controlled. A probable mechanism has been suggested for the decomposition process which agrees with the results obtained.