Reactivity of platinum nanoaggregates in catalytic reduction of U(VI) with hydrazine in acid solutions

Catalysts Pt/SiO₂ with different size of Pt nanoaggregates were studied in catalytic reduction of U(VI) with hydrazine in solutions of H₂SO₄, HClO₄, and HNO₃. The catalytic activity of the surface Pt atoms of Pt/SiO₂ in this reaction monotonically increases with an increase in the size of metal crystallites on the support, i.e., the negative size effect is observed. Catalytic reduction of U(VI) with hydrazine in H₂SO₄ solutions is significantly faster than in HClO₄ and HNO₃, and in HClO₄ it is slightly faster than in HNO₃. The results were interpreted within the framework of the concept of the energetic nonuniformity of the surface atoms and of the mechanisms of catalytic reduction of U(VI) with hydrazine in acid solutions.