Kinetics of the decomposition of hydrogen peroxide in alkaline solutions

Abstract

Hydrogen peroxide decomposition in 1-5 mol dm-3 KOH and 1-2 mol dm-3 NaOH solutions is a first-order reaction with respect to undissociated hydrogen peroxide. The decomposition is catalysed by compounds of heavy metals (Fe, Cu) present as trace impurities in these solutions and is first order with respect to them. The hydroxyl ion concentration exerts a significant effect on the decomposition rate, which has been explained by its influence on the activity of catalysing species having colloidal character, which are probably the active sites for the decomposition.The kinetics of hydrogen peroxide decomposition in dilute solutions of alkali hydroxides have been studied by many authors, especially with regard to using these solutions for bleaching cellulose and textile materials. However, the results of these studies are difficult to compare, as the spontaneous decomposition of peroxide is apparently a catalysed reaction whose rate is also affected by the nature and concentration of trace impurities present. It has long been known that bases accelerate the decomposition of peroxide and that the content of trace heavy-metal impurities has the principal influence on the reaction rate.l According to Biirki and Schaaf,2 peroxide decomposition in dilute alkali hydroxide solutions is a first-order reaction with respect to the peroxide, the decomposition rate increasing with increasing hydroxide concentration (from 5 x lo-* to 0.2 mol dm-3 NaOH). It was later found that peroxide decomposition is fastest at a ratio of peroxide concentration to that of hydroxide of t~0~-~ or three.6 From the former value, at which about one half of the peroxide is present as perhydroxyl ions, it was derived by AbeP that peroxide decomposition proceeds through the reaction of perhydroxyl ions with undissociated (A) peroxide molecules :HOT + H 2 0 2 -+ H 2 0 + 0, + OH-.The decomposition of peroxide in pure hydroxide solutions was considered to be an uncatalysed reaction, resulting from the oxidising properties of the peroxide molecules and the reducing properties of the perhydroxyl i o m 3 Similar dependences of the decomposition rate on the total alkalinity were found in pure solutions of potassium and sodium hydroxide in the presence and in the absence of colloidal catalysts (Pt, Au, Pd).3In agreement with the results of Abe13, Duke and Haas' found that the experimental dependence of the peroxide decomposition rate on the total alkalinity at a constant total peroxide content is analogous to the dependence of the product c(H202) c(H0;) on the total alkalinity. They concluded that peroxide decomposition obeys the equation where a is the total peroxide content in the solution and c(H20,) and c(H0,) are the concentrations of undissociated peroxide and perhydroxyl ions, respectively. Peroxide da/dt = k c ( H 2 0 2 ) c(H0,) 2349

Kinetics and Mechanism of Potassium Persulfate Decomposition in Aqueous Solutions Studied by a Gasometric Method

“…These facts suggest that the hypothesis: 2 HO e H 2 O 2 e H 2 O + 1/2 O 2 must be neglected because according to literature data [39,40] H + has very weak catalytic effect on H 2 O 2 decomposition rate, but in alkaline solutions H 2 O 2 decomposition is fast. Apart of this argument it must be taken into account that if H 2 O 2 is an intermediate O 2 must be degaged after an induction period, also the iodometrically determined remained (not reacted) P concentration seems to be greater because H 2 O 2 oxidizes I -ion as P anion does.…”

Stabilization of iron-catalysed hydrogen peroxide decomposition by magnesium

“…This "spontaneous" decomposition has been shown to be second-order with respect to peroxide concentration (4, 20). Many previous investigations on alkaline peroxide decomposition have noted the importance of purification of the alkali, as this is usually the source of metallic impurities (4,21). Semiconductor grades of sodium and potassium hydroxide containing very low levels of trace metals are now commercially available, and are well suited for this type of investigation.…”

“…Figure 3a shows that, for results at pH 1 1 .O, there is a non-line& relationship between time and the logarithm of peroxide concentration, unless only the initial reaction period is considered. Other studies have also recognized that this system is indeed more complex than can be represented by a simple first-order process (21,24). One analysis of kinetic data was interpreted on the basis of two parallel decomposition pathways (21 alkalinity of the solution for a given metal ion concentration, while the second was independent of the concentration of molecular hydrogen peroxide (2 1).…”

Efficient Mineralization of Paracetamol Using the Nanocomposite TiO2/Zn(II) Phthalocyanine as Photocatalyst

“…66,67 The coupling effects of the allowed transitions of these aggregates and electronic states of the bare TiO 2 -P25 leads to an improvement in the charge carrier mobility, favoring the electron transfer. [68][69][70] Vol. 27, No.…”