Electron-transfer at alumina surfaces: 4. Reduction of iodine

Abstract

The reduction of iodine to iodide ion occurs readily on the surface of partially dehydrated catalytic aluminas and silica-aluminas. An increase in the alumina content of the latter results in an increase in reducing activity. Replacement of the hydroxyl ion on the alumina surface by the fluoride ion decreases the reducing power. Two different surface sites are responsible for the reducing properties. For alumina samples dehydrated at low temperatures (<400 °C) the reducing site appears to be the hydroxyl ion, whereas at higher activation temperatures a defect site involving oxide ions probably acts as the electron donor. These findings concur with those reported from an earlier study of the reduction of tetracyanoethylene on the alumina surface.