Using density functional theory and cluster expansion-based Monte Carlo simulations, we examine the effect of Pd dispersion on the energetics and barriers for the reaction of O2 with H atoms to form H2O and H2O2 on a AuPd/Pd(1 1 1) alloy surface. Our calculations show that this hydrogenation reaction is considerably affected by the distribution of Pd and Au atoms in the surface layer. In particular, on isolated Pd monomers surrounded by less active Au atoms, the activation barrier to form H2O2 is appreciably lowered due to the suppression of O-O bond cleavage. In contrast, the reactivity to H2O on the Pd dimer is predicted to be enhanced compared to pure Pd. Using Monte Carlo simulations we also predict Pd ensemble populations in the AuPd surface layer as a function of temperature and composition. Due to the favorability of Au-Pd interactions over Pd-Pd, we find that small ensembles, particularly monomers, preferentially exist. This study highlights how theoretical investigation of bimetallic alloys, particularly the surface arrangement of atoms and the influence of ensembles on reaction energetics, can offer insight into the design of catalysts and tailoring of reaction conditions.
Bibliographical noteFunding Information:
This work was supported by the R. A. Welch Foundation (F-1535). The authors also thank the Texas Advanced Computing Center for use of their computing resources.
- Cluster expansion method
- Density functional theory
- Ensemble effect
- Monte Carlo
- Oxygen reduction reaction
- PdAu alloy catalyst