The thermal decomposition of hydrogen peroxide, H(2)O(2), was determined in aqueous suspensions of SiO(2), Al(2)O(3), TiO(2), CeO(2), and ZrO(2) 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 H(2)O(2) independent of the type of oxide. Oxide type had a strong effect on the pre-exponential rate term with increasing rate in the order of SiO(2) < Al(2)O(3) < TiO(2) < CeO(2) < ZrO(2). The rate coefficient for H(2)O(2) 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 H(2)O(2) gaseous decay product, suggesting that decomposition occurs on the oxide surfaces. The decomposition of H(2)O(2) 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.
