Surface structures formed on cobalt oxide during catalytic oxidation: An infrared study

Abstract

Reaction intermediates formed on cobalt oxide (Co 3O 4) during catalytic oxidation have been studied using infrared spectroscopy. The adsorption of CO, CO 2, ethylene, cyclohexane, cyclohexene, oxygen, H 2O, D 2O, H 2O 18, and various mixtures of these gases was investigated. The adsorption of CO or CO 2 at room temperature was found to give rise to a bidentate carbonate surface complex which, for the most part, converts to a monodentate species when water is introduced to the sample. No hydrocarbon entities were found to exist on cobalt oxide from infrared analysis, indicating that only minor amounts of these compounds are adsorbed, if at all, on the surface at any specific time. Carbonate reaction intermediates were observed (plus water formed by the oxidation reaction) only when cobalt oxide samples were heated to approximately 325 °C in the presence of a hydrocarbon. The amount of carbonate intermediate found when hydrocarbon-oxygen mixtures were introduced to freshly degassed cobalt oxide samples was quite small at room temperature, increased substantially when the sample was heated to about 200 °C, and showed further increases in adsorbed material when the samples were heated to 325 °C in the hydrocarbon-oxygen mixtures.