Catalytic decomposition of hydrazine in weakly alkaline solutions on platinum nanoparticles

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...

Luminol chemiluminescence catalysed by colloidal platinum nanoparticles

“…Colloidal platinum nanoparticles as catalysts for electron-transfer reaction were extensively investigated (27)(28)(29). Furthermore, Aiuchi (30) and Anan'ev (31) reported that colloidal platinum nanoparticles as a catalyst could transfer electrons to hydrogen peroxide and hydrazine to cause them decompose in weakly alkaline solutions. As for the mechanism of hydrogen peroxide decomposition, many possible mechanisms for this catalysis have been proposed.…”

Pt‐Catalyzed Formation of Ni Nanoshells on Carbon Nanotubes

“…However, the catalytic decomposition of hydrazine in the presence of platinum nanoparticles can take place on the surface of these nanoparticles by an electrophilic addition, that is, by forming electrophilic radicals which can then react with other hydrazine molecules from solution. [18] The presence of metallic platinum nanoparticles therefore implies the reduction of nickel complexes without the need for additional hydroxy groups present in solution. In fact, we observed that reduction of Ni 2+ did not occur in experiments using PAHfunctionalized CNTs in the absence of Pt nanoparticles.…”

Quasi‐Epitaxial Growth of Ni Nanoshells on Au Nanorods

“…Thus, the presence of Pt on the Au rods was essential to achieve the catalytic effect in nickel reduction and shell formation. The catalytic role of platinum seems to be related to the decomposition of hydrazine on the small nanoparticles, as discussed by Ershov et al, [37] who suggested the release of electrophilic radicals, which can react with other hydrazine molecules in solution. In the present case, in which hydrazine is partly complexed with Ni 2+ ions, [38] most of the non-complexed hydrazine can be catalytically decomposed on the platinum surface, leading to a charged metallic surface, where the Ni II complexes can be easily reduced to Ni 0 .…”