The platinum catalyzed hydrazine decomposition in non-nitrate acidic media

Abstract

The stoichiometry, kinetics and the mechanism of the hydrazine decomposition over the 1% Pt/SiO 2 catalyst in the solutions of perchloric and sulphuric acids were studied at [N 2H 5 +] 0 = 2×10 −3 to 0.25 M; [H +] = ∼10 −4 (pH 4) to 3.4 M (HClO 4 or H 2SO 4); T=40–90 °C; and a solid:liquid ratio, S/L=0.02–0.2 g/ml. It was shown that the hydrazine catalytic decomposition proceeds with a formation of the ammonium ions and the gaseous nitrogen as reaction products in all studied range of the experimental conditions. It was found that the apparent reaction order with respect to [N 2H 5 +] depends on the hydrazine initial concentration and increases from about 0.2 to 1 when [N 2H 5 +] 0 decreases from 0.2 to 0.01 M. The reaction deceleration and the increase of the apparent activation energy with the increase of the solution acidity is explained by the competitive adsorption of the hydrogen ions on active catalyst centers. The mechanism of the hydrazine heterogeneous catalytic decomposition in acid non-nitrate solutions includes the adsorbed hydrazine dissociation as a limiting step of the reaction.