Decomposition of hydrogen peroxide at water-ceramic oxide interfaces

The thermal decomposition of hydrogen peroxide, H2O2, was determined in aqueous suspensions of SiO2, Al2O3, TiO2, CeO2, and ZrO2 nanometer-sized particles. First-order kinetics were observed for the decomposition in all cases. Temperature dependence studies found that the activation energy was 42 +/- 5 kJ/mol for the overall decomposition of H2O2 independent of the type of oxide. Oxide type had a strong effect on the preexponential rate term with increasing rate in the order of SiO2 < Al2O3 < TiO2 < CeO2 < ZrO2. The rate coefficient for H2O2 decomposition increases with increasing surface area of the oxide, but the number or efficiency of reactive sites rather than the total surface area may have the dominant role. Very efficient scavengers for OH radicals in the bulk liquid are not able to prevent formation of molecular oxygen, the main H2O2 gaseous decay product, suggesting that decomposition occurs on the oxide surfaces. The decomposition of H2O2 in the gamma-radiolysis of water is enhanced by the addition of ceramic oxides, possibly due to excess formation of hydrated electrons from energy deposited in the solid.