High Catalytic Activity of Singly Distributed Pd₁/ZnO(10-10) toward Methanol Partial Oxidation: A DFT based Accelerated Kinetic Monte Carlo Study

We have performed accelerated kinetic Monte Carlo (KMC) simulations for methanol partial oxidation on Pd₁/ZnO(10-10) and Pd₁₆Zn₁₆ nanocluster systems based on the energetics and kinetic parameters derived from our recent density functional theory (DFT) calculations for both systems. In agreement with recent experiment [1] our simulations confirm that H₂ selectivity of the singly dispersed Pd₁/ZnO is ~97%, by far higher than that of Pd₁₆Zn₁₆, only ~50%. Our combined DFT+KMC simulations provide insights into high activity and selectivity of Pd₁/ZnO. We find that singly-distributed Pd sites induce substantial modification of the local geometrical and electronic structures of Zn sites. Singly distributed Pd sites serve as the active sites for H₂ adsorption. Furthermore, they provide the strong adsorption for methanol, induce the spontaneous CO₂ formation and nearly spontaneous dissociation of H₂O, and the stabilization of H₂ right at or near the sites, thereby decisively enhancing H₂ and CO₂ selectivity. For Pd₁/ZnO catalyst, we find that CO₂ formation occurs via O*+CO*→CO₂* and an alternative pathway (dissociation of H₂COO* and HCOO*) is kinetically unfavorable.
[1] F. F. Tao et al, private communication