Initial Reduction of the PdO(101) Surface: Role of Oxygen Vacancy Formation Kinetics

We investigated the initial thermal reduction of the PdO(101) surface using density functional theory (DFT) calculations. The defect-free PdO(101) surface consists of parallel rows of undercoordinated Pd and O atoms (Pdcus and Ocus, respectively). DFT was used to map out the elementary processes of Ocus vacancy formation, oxygen surface atom diffusion along the Pdcus rows, and various O2 formation pathways. Because oxygen vacancies form during the reduction of the surface, the elementary processes were examined with and without the presence of adjacent Ocus vacancies. DFT calculations show that the presence of oxygen vacancies strongly affects the barriers of adjacent surface processes. Barriers for O vacancy formation are reduced by nearly 50% with an adjacent O vacancy. The barrier for O2 formation along the Pdcus row drops from 1.54 eV on the defect-free PdO(101) surface to 0.81 eV in the presence of an Ocus vacancy dimer. However, the presence of Ocus vacancies also leads to more strongly bound O2 on ...