Using quantum chemical modeling with periodic boundary conditions we investigated deposited platinum clusters and isolated ions on cerium dioxide support and CO adsorption and oxidation on them. As the catalytic behavior of supported platinum species depends on their nuclearity under the reaction conditions we compared the stability of the platinum clusters with respect to decomposition to Pt0, Pt0(CO) and/or Pt2+(CO)2 in the presence of CO. Ceria was modeled as regular slab of CeO2(111) surface and as ceria nanoparticle. While the decomposition of pristine platinum clusters to neutral atoms in absence of CO is endothermic on both ceria supports, at complete coverage of the cluster with CO the formation of Pt0(CO) monocarbonyls is essentially energy-neutral. In addition, on ceria nanoparticle formation of Pt2+(CO)2 species is favorable due to the presence of low-coordinated O centers, where the complex is coordinated, and easily reducible Ce4+ ions. Thus, under CO pressure platinum clusters may decompose to neutral monocarbonyls on the ceria surface and to cationic complexes on the ceria nanoparticle. Due to the high catalytic activity of the Pt/CeO2 systems in low-temperature CO oxidation, we have modeled transition state structures for oxidation of CO molecule in such system. We modeled the process on the deposited platinum cluster with different CO coverage and on mononuclear platinum cations in different oxidation states. We also considered different origins of the oxygen center involved in the oxidation - from a dissociated oxygen molecule at the platinum center or from a surface oxygen center of cerium dioxide. The results suggests that one may find transition states with similar activation energy on the supported platinum clusters and ionic platinum species. Thus, the results suggests that the catalytic oxidation may occur both on platinum clusters and on isolated platinum ions on ceria surface or ceria nanoparticles. The calculations were performed with DFT+U approach using periodic code VASP with the gradient corrected PW91 exchange-correlation functional. The valence wave functions were expanded in a plane-wave basis with a cutoff energy of 400 eV.

Computational modeling of stability and properties of cerium dioxide supported platinum clusters and isolated platinum species

2019 Spring National Meeting

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