Autocatalytic Reduction of a Cu2O/Cu(111) Surface by CO: STM, XPS, and DFT Studies

The reduction of a Cu2O surface layer on Cu(111) by CO was studied using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and calculations based on density functional theory. Real-time XPS measurements show the existence of an induction time and an autocatalytic reaction for the reduction of the Cu2O/Cu(111) surfaces. The reduction of the Cu2O surface layer goes through two stages, the "slow reaction" regime and the "fast reaction" regime. During the "slow reaction" regime, an "O-deficient Cu2O" phase forms and propagates on the surface. which lowers the reaction barrier for the removal of lattice oxygen in Cu2O. The propagation of the "O-deficient Cu2O" phase across the surface leads to the "fast reaction" regime, through which the reduction rate is approximately constant clue to a "step-only" reaction mechanism. STM studies provide an atomic level picture for the intermediate structures and the reaction pathway during the reduction of the CU2O surface oxide. Upon the loss of chemisorbed oxygen from the typical Cu2O honeycomb structure, a reconstruction occurs, and Cu2O heptagons are formed. The "O-deficient Cu2O" phase is a disordered phase linked to the formation of. Cu2O heptagons. The Cu2O heptagons provide adsorption sites for CO, which reacts with chemisorbed oxygen hopped from neighboring Cu2O honeycombs.