Oxidation of Carbon Monoxide and Methyl Alcohol photosensitized in the Gas Phase by Zinc Oxide

Abstract

THE well-known photosensitizing action of zinc oxide in oxidation reactions, where oxygen was considered to be the reactant photoactivated in the process and the sensitivity of certain gases in affecting and being affected by the concentration of holes or electrons in semiconductor catalysts led us to examine the possibility of carrying out the photocatalysis of carbon monoxide and methyl alcohol oxidations in the gas phase, the latter giving rise to the former as a secondary phase in the oxidation. This has been done in a dynamic reaction system containing zinc oxide (sulphur content = 0.01 per cent) supported on a quartz frit inside a quartz reaction vessel through which purified oxygen at atmospheric pressure saturated with methyl alcohol vapour at 20° C. (pMeOH = 95.2 mm.) was passed continuously. When the zinc oxide was subjected to radiation emitted from an a.c. 220-V. 2.4-amp., high-pressure quartz mercury vapour lamp kept parallel to the layer of zinc oxide powder on the quartz frit at a distance of 5 cm. the photocatalytic oxidation of methyl alcohol could indeed be induced readily at temperatures ⋝ 70° C. In the absence of irradiation, the oxidation of methyl alcohol catalysed by zinc oxide under identical conditions was observed at and/or above 250° C. only.