The reaction routes between co-adsorbed CO and O on kinked Au(321) slabs are analyzed theoretically. Complexes of vicinal type react most easily with calculated barriers from 0.05 to 0.3 eV, whereas the more strongly co-adsorbed geminal structures do not react directly unless surface oxygen is present in excess. Generally, the activation energy of CO2 formation from vicinal complexes remains low and that from geminal complexes increases, when Ag impurities are introduced. Our results can be generalized to other rough gold surfaces, particularly, helping to understand the formation of CO2 above 200 K, as observed in the temperature programmed desorption studies of nanoporous gold, a monolithic nano-structured gold catalyst. (C) 2011 Elsevier B. V. All rights reserved.