Some physical and catalytic properties of cerium dioxide-nickel oxide two-component catalysts have been studied over the entire composition region, employing the decomposition of hydrogen peroxide in aqueous solution as a model catalytic process. The two oxides have been found to affect each other, particularly for NiO contents of 9.1 and 96.7 mol%; the mutual influencing, the nature of which in the conditions applied remains unaffected by heat treatment of the sample or by its exposition to ionizing radiation, is manifested by the nonmonotonic dependences of the oxidation power and of the specific activity of the catalysts on their composition. This can be interpreted in terms of the concept of bivalent catalytic centres, assuming that for nickel oxide the centres consist of Ni2+-Ni3+ ion pairs, for cerium dioxide they consist of Ce3+-Ce4+ ion pairs, and that in the region of the mutual influencing , Ni2+-Ce4+ ion pairs play a major role. Within the scope of this concept, the increase in the oxidation power of all the catalysts in question and a simultaneously decrease in the specific activity of the pure nickeloxide exposed to ionizing radiation can be explained in terms of the ionization effect.
Effects of Humic Substances on the Aqueous Stability of Cerium Dioxide Nanoparticles and their Toxicity to Aquatic Organisms