Kinetics and mechanism of the color removal from congo red with hydrogen peroxide catalyzed by supported zirconium oxide

The kinetics of the oxidative color removal from congo red dye using H2O2 i n conjunction with transition metal ions supported on ZrO2 were studied. Th e rate of reaction is first order on H2O2, the catalyst, and in congo red. It attains a limiting rate at higher concentrations of reagent. Also, the r ate of reaction decreases with increasing [H+], due to protonation of the s ubstrate amino groups, as well as to the low deprotonation constant of H2O2 in acid medium. Addition of KCl to the mixture increased the rate of react ion. The catalytic activity of the catalysts lies in the following order: A g-I > Cu-II > Hg-II > Co-II > Mn-II > Fe-III > Ni-II > ZrO2 which is correl ated with the redox potential, mg loading and % surface content of the supp orted metal ions. A probable mechanism for the oxidation processes has been suggested, which is consistent with the experimental results.