High Selectivity and Activity of Ti-Cu(111) Dilute Alloys for the Deoxygenation of Ethanol to Ethylene

Dilute Ti-Cu(111) alloys are found to be highly selective for converting ethanol to ethylene. Temperature-programmed reaction spectroscopy (TPRS) shows that adsorbed ethanol deoxygenates on Ti-Cu(111) surfaces with ∼10% Ti to produce gaseous C2H4 and H2 at temperatures near 400 K. Scanning tunneling microscopy and vibrational spectroscopy of adsorbed CO demonstrate that Ti surface sites are oxidized to TiO x by reaction with ethanol, causing the reaction selectivity to change from C2H4 to acetaldehyde production during repeated TPRS experiments with ethanol. TPRS simulations derived from density functional theory (DFT) calculations confirm that Ti ensembles within the Cu(111) surface layer promote ethanol deoxygenation at moderate temperature and reveal a significant enhancement in the activity and selectivity for gaseous C2H4 and H2 production as the Ti ensemble size is increased from monomer to trimer. DFT shows that increasing the Ti n ensemble size from n = 1 to 3 increases the stability of the adsorbed O atom released during C–O bond cleavage, thus facilitating ethanol deoxygenation. The calculations show that the O atom bound to Ti further enhances C2H4 production by destabilizing the adsorbed C2H4 and its dehydrogenation product and that this destabilization effect becomes more pronounced as the Ti ensemble size is increased from monomer to trimer. Our results demonstrate that dilute Ti-Cu(111) alloys promote the conversion of ethanol to ethylene at moderate temperature and reveal that this surface chemistry is strongly influenced by the Ti ensemble size and the adsorbed O atom released during C–O cleavage.