High Resolution Image Download MS PowerPoint Slide The mechanisms for the oxidation of CO catalyzed by Fe-modified CeO 2 surfaces have been investigated using periodic density functional theory calculations corrected for the on-site Coulomb interaction by a Hubbard term (DFT + U ). The following findings were made: (i) Fe is stable both as an adsorbed atom, Fe δ+ (δ < 2), on the surface and as a dopant, Fe 3+, in the surface region. (ii) The Fe dopant facilitates oxygen vacancy formation, whereas Fe adatoms might suppress oxygen vacancy formation. (iii) In addition to physisorbed CO as on the clean surface, physisorbed CO 2 and chemisorbed CO (carbonate, CO 3 2– ) species are observed on the Fe-doped CeO 2 (111) surface. Vibrational frequency calculations were carried to characterize these species. (iv) CeO 2 (111) containing positively charged Fe ions, either as supported isolated Fe δ+ adatoms [or small Fe x δ+ ( x = 2–5) clusters] or as substitutional Fe 3+ ions, was found to catalyze the conversion of CO to CO 2 . Incorporating Fe 3+ ions into the ceria lattice as substitutional point defects can instead sustain a full catalytic cycle for CO oxidation and catalyst regeneration. The Fe dopant promotes multiple oxidations of CO without any activation energy, leading to O vacancy formation and CO 2 desorption. Molecular O 2 adsorbs at the O vacancy, forming O adspecies that then drive CO oxidation and recover the stoichiometric Fe-doped CeO 2 surface. A Bader charge analysis was carried to characterize the oxidation state of Fe ions along the catalytic cycle.
No takes yet. Share an insight, caveat, or question.
Chen et al. (2011) studied this question.