Catalytic Reduction of Np(VI,V) with Formic Acid in Perchloric Acid Solutions

Neptunium(VI) is successively reduced with formic acid to Np(V) and Np(IV) in perchloric acid solutions in the presence of 1% Pt/SiO₂ catalyst. The kinetic features of Np(VI,V) reduction with formic acid in 0.1-4.0 M HClO₄ in the presence of 0.01-0.1 g ml^-1 of 1% Pt/SiO₂ at [HCOOH] = 0.001-1.0 M and T = 40-70°C were studied. The rate-determining steps of reduction of Np(VI) to Np(V) and Np(V) to Np(IV) are diffusion and decomposition of the activated complex adsorbed on the catalyst surface, respectively. The mechanisms of both processes are discussed.