First-principles investigations of O2 dissociation on low-coordinated Pd ensembles over stepped Au surfaces

The adsorption and dissociation of O-2 on Pd monomer or trimer incorporated into Au(322) and Au(321) surfaces are systematically investigated by first-principles calculations and nudged-elastic-band simulations. We found that the contiguous low-coordinated Pd ensembles alloyed into step edges of Au surfaces are required for O-2 dissociation with an enhanced adsorption energy (similar to-1.00 eV). The dissociative barrier of O-2 is mainly related to the size of Pd ensembles, and the activation energy is about 1.00 eV on Pd trimers. However, the Pd monomer is less active for the adsorption and dissociation of O-2. Additionally, the O spillover from Pd to Au sites only occurs at elevated temperature, and the diffusion processes are highly endothermic. The calculated results indicate that the Pd-modified Au step edge with a contiguous Pd ensemble is the reactive center for supplying atomic oxygen on Pd-doped Au catalysts. (C) 2012 Elsevier B.V. All rights reserved.