Catalytic reduction of Np(VI) with formic acid in the presence of platinum nanoparticles

Abstract

The kinetics of catalytic reduction of Np(VI) with formic acid in the presence of Pt nanoparticles of different types (“brown” colloid stabilized with sodium polyacrylate and nonstabilized “gray” colloid) was studied. In both cases in the examined range of conditions ([Np(VI)]₀ = 2.80 × 10⁻⁴−9.03 × 10⁻⁴ M; [HCOOH] = 0.03–1.0 M; [Pt] = 4 × 10⁻⁷ −2 × 10⁻⁵ M; T = 18–60°C) the reaction is zero-order with respect to [Np(VI)] and first-order with respect to [HCOOH]. The catalytic activity of the nonstabilized “gray” colloid exceeds by almost an order of magnitude that of the “brown” colloid, due to the blocking effect of stabilizing polyelectrolyte molecules on the active catalytic centers. The dependence of the reaction rate on the sodium polyacrylate concentration in the range 1 × 10⁻⁴−1 × 10⁻² M is nonmonotonic, due to deflocculation of the nanoparticles. The mechanism of the catalytic reduction of Np(VI) with formic acid in the presence of Pt colloids is discussed; it involves a slow step of dissociative chemisorption of HCOOH molecules on the nanoparticle surface.