The decomposition of peroxides. Part I. Kinetic studies of the decomposition of hydrogen peroxide vapour on copper(I) oxide–copper single crystals

Abstract

The decomposition of hydrogen peroxide vapour has been examined from 60 to 160° on copper(I) oxide supported on copper single-crystals in a flow system. For partial pressures of hydrogen peroxide up to 1·13 mm. at 98° and below, kinetic studies indicate the relation: –dp(H₂O₂)/dt=k.p(H₂O₂)/p^½(H₂O) for the reaction rate on thin oxide films grown on the (100), (110), and (111) faces of high-purity copper. Above 98°, the rate dependence on p(H₂O) gradually diminishes. Thus, at 117°, rate ∝p^–0·10(H₂O), and at 160°, rate ∝p^–0·05(H₂O). These relationships were independent of the orientation of the copper crystal. The activation energy of the decomposition had three values clearly related to temperature range. Thus, for a copper(I) oxide film, 100–300 Å thick, supported on a (111) copper face, E_a= 16·0, 21·0, and 8·0 kcal. mole^–1 from 80 to 98, 98 to 117, and 117 to 160°, respectively. The orientation of the copper crystal face slightly affects these E_a values.

The effects on catalyst activity of a variation in surface treatments, such as achieved by electro- and mechanical polishing and by oxide film growth up to 1000 Å, have also been studied. A reaction mechanism is proposed to account for the observed experimental rate data. Its validity depends on the occurrence of surface poisoning reactions through adsorption of OH^– and O₂H^– radicals which may lead to the formation of transient hydroxide species.