No abstract

The kinetics and stoichiometry of catalytic decomposition of hydrazine in 0.01 M NaOH solutions in the presence of unstabilized ([gray] colloid) and stabilized with sodium polyacrylate ([brown] colloid) platinum nanoparticles were studied. The main decomposition products are ammonia and N 2 with H 2 impurity (up to 1.5%), i.e., hydrazine decomposition predominantly follows the stoichiometric equation 3N 2 H 4 = 4NH 3 + N 2 . The catalytic activity was studied as influenced by nanoparticle size distribution. Despite higher nanoparticle dispersion, the catalytic activity of the stabilized [brown] colloid is lower than that of the [gray] colloid. The reaction mechanism is discussed.Owing to high reduction activity, hydrazine is widely used in wet processes of the nuclear fuel cycle as stabilizer of actinide ions in lower oxidation states [1] or as nitrite scavenger [2]. The presence of hydrazine in aqueous waste is undesirable, because it often complicates treatment of liquid radioactive waste, in particular, in the course of chemical denitration [3]. It was found [4 3 6] that hydrazine is effectively decomposed in the presence of finely dispersed platinum catalyst supported on silica. However, this Pt/SiO 2 catalyst can be used only in acidic solutions because of low chemical stability of the support (silica) in alkaline and carbonate solutions. Hence, search for new catalytic materials stable in the above media is of particular importance.Colloids of platinum group metals are highly selective catalysts for many chemical reactions [7,8]. Platinum nanoparticles exhibit catalytic properties both in oxidation (e.g., of 2-propanol [9]) and reduction (reaction of molecular hydrogen with methylviologen [10]) processes. It was found [10] that the catalytic activity of platinum nanoparticles prepared by various procedures is considerably different.In this work we continued a study of the catalytic properties of platinum nanoparticles, with hydrazine decomposition in weakly alkaline solutions as example. EXPERIMENTAL Preparation of Platinum Nanoparticles and Their PropertiesCatalytic decomposition of hydrazine was studied using two types of colloids prepared by different procedures.In the first procedure, colloidal platinum was prepared directly in the reaction system by injection of an aliquot of H 2 PtCl 6 solution into a temperaturecontrolled working solution of sodium hydroxide (10 32 NaOH) containing excess hydrazine. In this case, platinum was rapidly reduced to the finely dispersed metal and the solution became gray due to platinum colloid; the [gray] colloid was stable within the entire experimental time. This colloid catalyzed decomposition of excess hydrazine.In the second case, platinum nanoparticles were prepared according to the standard procedure [10] by reduction of H 2 PtCl 6 or K 2 PtCl 6 in 10 32 M NaOH solution with molecular hydrogen in the presence of sodium polyacrylate stabilizer. As a result, stable brown colloidal solution was prepared ([brown] colloid).The size distributions of platinum nanopa...

No abstract

No abstract

No abstract