Impact of Sm3+ Ions on Oxygen Vacancy Formation in Ceria Systems

DFT calculations have been employed to investigate the impact of Sm dopant(s) on the structure and stability of periodic CeO2(111) slab and Ce140O280 nanoparticle systems. We found that substituting Ce ion(s) with Sm ion(s) in the surface layer yields the most favorable doped configurations in both systems. Further, we evaluated how Sm ion(s) modify the reducibility of the systems—a key process in the catalytic applications of ceria. It has been found that a substantial reduction in oxygen vacancy formation energy occurs due to the presence of Sm ion(s), with values of 1.24 and 0.29 eV for mono- and bi-doped CeO2(111), respectively, which are considerably lower than 2.43 eV obtained for the pristine ceria slab. As the system changes from slab to nanoparticle, mono-doping reduces this energy to 0.25 eV—about four times lower than that calculated for the pristine Ce140O280 nanoparticle. The presence of a second Sm ion within the nanoparticle leads to a dramatic decrease in Evac, making the reduction process exothermic. In either slab or nanoparticle models, the Sm3+ ions prefer to be in close proximity to each other, and the formation of oxygen vacancies is most energetically favorable in the vicinity of Sm3+ ions.