Reaction of ethanol on oxidized and metallic cobalt surfaces

摘要

The reaction of ethanol on metallic and oxidized cobalt surfaces was studied using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) in order to determine the dependence of the reaction pathways on the cobalt oxidation state. The primary reaction for ethoxide species on metallic cobalt surfaces was decarbonylation producing CO, H_2 and carbon. This reaction was facile and occurred below 400 K. In contrast, CoO_x surfaces which predominantly contained Co~(2+) were selective for the dehydroge-nation of ethoxide groups to produce acetaldehyde at 400 K. A fraction of the acetaldehyde molecules produced by this pathway were further oxidized to acetate which decomposed to produce CO_2 at 495 K. More highly oxidized Co surfaces that contained both CO~(2+) and Co~(3+) were active for the complete oxidation of ethanol producing CO, CO_2, and H_2O as the primary products. The insights that these results provide for understanding the mechanism of the steam reforming of ethanol on cobalt catalysts is discussed.