The decomposition of peroxides. Part II. The effects of deformation and contamination of copper(I) oxide–copper surfaces on the decomposition of hydrogen peroxide vapour

Abstract

The decomposition of hydrogen peroxide vapour has been studied from 60 to 140 °C on single crystal faces of high-purity copper supporting copper(I) oxide. Crystals were damaged and stressed by either mechanical techniques or neutron irradiation. The effects of these treatments on catalyst activity were determined and the results related to apparent dislocation densities as measured by chemical etching. Results indicate that the introduction of an added number of dislocations, e.g., 4 × 10³ cm^–2 by fresh scratching, causes a measurable but small increase in activity. This increase is temporary and is lost after continued exposure to peroxide vapour during temperature cycling and also after annealing in hydrogen at 760 °C.

Activity results have been obtained also for crystal surfaces treated with gaseous hydrogen sulphide or chlorine when surface films of α-Cu_1·80S/Cu_1·96S and CuCl₂ were formed as shown by X-ray measurements. While the chloride catalysts had enhanced activity, the sulphide film acted as a poison unless the toxicity was removed by exposure to peroxide vapour for 12–26 h. This effect is thought to be due to the gradual formation of sulphate–type surface species through the reaction of the sulphide film with oxygen from the decomposition products. The reaction-rate dependence on the partial pressures of hydrogen peroxide, oxygen, and water vapour has been determined for the chemically treated surfaces along with activation energies. These data are interpreted in terms of the previously evaluated mechanism where rate control is associated with surface poisoning by hydroxyl ions.