Shift in binding site preference during oxygen adsorption on Au(111) at higher coverages and its impact on the...

Adsorbed oxygen plays a critical role in gold catalysis and it participates as an active species in many industrial reactions. We explore the oxygen adlayer phases on gold as a function of coverage and temperature in this work. The phase diagram of O/Au(111) is determined using cluster expansion based kinetic Monte Carlo (KMC) simulations over a coverage range of 0.05-0.45 ML for conditions relevant to room temperature catalysis. Both fcc and hcp adsorption sites are considered in our calculations. The KMC simulations reveal the coexistence of three ordered surface phases, namely, p(√7 × √7)R19.1°, p(2 × 2) and p(√3 × √3)R30°-2O at temperatures of 200-400 K. Although fcc sites are preferred at low O coverages, hcp sites can also become favorable at higher coverage. This study improves our understanding of the local oxygen arrangements on the Au(111) surface, and provides a theoretical basis for identifying reactive O sites for catalytic reactions.