Ethanol dehydrogenation and autocatalytic dehydration on oxidized Cu(111)

Abstract

Exploring the formation of valuable chemical feedstocks from renewable sources is critical for decreasing global dependence on fossil fuels. The decomposition of ethanol forms acetaldehyde, a solvent and precursor for dyes, pesticides, pharmaceuticals and more; ethylene, which is crucial for the plastics industry; and clean hydrogen, a necessity for all hydrogenation reactions. While it is well known that Cu(111) and oxidized Cu(111) catalyze the dehydrogenation of small primary alcohols to form aldehydes, dehydration products to form alkenes are less discussed. An in depth study of the reactivity of ethanol on O/Cu(111) shows dehydrogenation, dehydration, and combustion products using temperature programmed reaction spectroscopy (TPRS). The presence of oxygen on O/Cu(111) resulted predominantly in acetaldehyde formation via the dehydrogenation pathway, with lesser amounts of ethylene via dehydration, as well as combustion products. Successive TPRS experiments resulted in decreased yields of all products due to the consumption of surface oxygen via water formation <200 K. Isotopic studies of ethanol–OD indicate the role of the hydroxyl hydrogen in water formation from O_ads compared to water that desorbs during dehydration, as well as hydrogen formation via the dehydrogenation pathway. The dehydration pathway is proposed to occur via autocatalytic production of O_ads during the ethoxy transformation to ethylene, furthering the reaction to form ethylene and CO₂.