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 selectivefor convertingethanol to ethylene. Temperature-programmed reaction spectroscopy(TPRS) shows that adsorbed ethanol deoxygenates on Ti-Cu(111) surfaceswith & SIM;10% Ti to produce gaseous C2H4 andH(2) at temperatures near 400 K. Scanning tunneling microscopyand vibrational spectroscopy of adsorbed CO demonstrate that Ti surfacesites are oxidized to TiO x by reactionwith ethanol, causing the reaction selectivity to change from C2H4 to acetaldehyde production during repeated TPRSexperiments with ethanol. TPRS simulations derived from density functionaltheory (DFT) calculations confirm that Ti ensembles within the Cu(111)surface layer promote ethanol deoxygenation at moderate temperatureand reveal a significant enhancement in the activity and selectivityfor gaseous C2H4 and H-2 productionas the Ti ensemble size is increased from monomer to trimer. DFT showsthat increasing the Ti- n ensemble sizefrom n = 1 to 3 increases the stability of the adsorbedO atom released during C-O bond cleavage, thus facilitatingethanol deoxygenation. The calculations show that the O atom boundto Ti further enhances C2H4 production by destabilizingthe adsorbed C2H4 and its dehydrogenation productand that this destabilization effect becomes more pronounced as theTi ensemble size is increased from monomer to trimer. Our resultsdemonstrate that dilute Ti-Cu(111) alloys promote the conversion ofethanol to ethylene at moderate temperature and reveal that this surfacechemistry is strongly influenced by the Ti ensemble size and the adsorbedO atom released during C-O cleavage.