The reactive nature of the polycrystalline zinc oxide surface has been investigated using methyl formate and ethanol as probe molecules; these have shown the dominant influence of the cation–anion dual site. Methyl formate decomposes during adsorption at the dual site to adsorbed methoxy and formate species. On temperature programming these show identical kinetics and reaction pathways to the methoxy and formate species observed previously after the adsorption of formaldehyde or methanol. Adsorption of ethanol at the dual site results in the formation of an adsorbed ethoxy species. On temperature programming, at 510 K, the zinc oxide surface abstracts one of the β-hydrogen atoms to form an unstable C₂H₄O fragment which decomposes mainly (90%) to ethylene; a small amount (ca. 10%) of the desorbing material which is either acetaldehyde or ethylene oxide (these cannot be distinguished by mass spectrometry) is desorbed coincidently at this temperature in an isomerization/desorption step. Despite the ethylene formation being a dehydration reaction, no water is observed in the desorption spectrum, the ethoxy oxygen species being left on the surface during decomposition.