Study of active surface centers of Pt/CeO₂ catalysts prepared using radio-frequency plasma sputtering technique

RF-plasma deposition of Pt on a nanosized ceria powder support has been performed directly in photoelectron spectrometer chambers to prepare model catalysts. The plasma deposition in an oxidizing environment results in the formation of highly dispersed oxide nanoparticles up to 2 nm large, which contain platinum solely as Pt⁴⁺ ions revealed by E_b(Pf4f_7/2) = 74.6 eV. Thus prepared model catalyst samples arranged as (sub-monolayer) films of PtO₂ nanoparticles on the surface of CeO₂ are characterized by an increased thermal stability compared with PtO₂ nanoparticles deposited on more inert supports. These PtO₂/CeO₂ model catalysts show a high activity in the CO oxidation even at room temperature. A detailed analysis of the O1s spectra obtained during the titration by CO of PtO₂/CeO₂ films strongly suggests that the reactive oxygen species are manifested with E_b(O1s) = 530.8 eV and 532.9 eV. The latter core level energies are attributed to oxygen in the platinum dioxide and to peroxide-like oxygen, presumably located at the interface between PtO₂ and CeO₂ particles. Results of our density-functional calculations indicate that the peroxide-like species can be energetically stabilized at the PtO_x–CeO₂ interfaces.