Reducible oxides represent an important class of catalytically active materials capable of releasing and storing atomic oxygen under dynamic operating conditions. When used as a support for noble metal nanoparticles, numerous phenomena arise due to electronic metal-support interaction such as the charge transfer between the metal nanoparticles and the support, adsorbate spillover, anchoring of atomically dispersed metals on the support, and reactive metal-support interactions. We show that these phenomena can be understood at the atomic level using a broad range of experimental techniques including photoelectron spectroscopies (XPS, SRPES), resonant photoemission spectroscopy (RPES), and scanning tunneling microscopy (STM) in combination with well-defined model Pt/CeO2 catalysts. In particular, we quantified the charge transfer between Pt nanoparticles and the support experimentally at particle sizes relevant for heterogeneous catalysis. Our method is based on the estimation of the density of Ce3+ centers formed upon charge transfer from Pt and enables us to “count” the number of electrons transferred per Pt particle. Using a similar approach, we explored the phenomenon of reverse oxygen spillover associated with the self-cleaning properties of ceria-based catalysts. Furthermore, we investigated stability of atomically dispersed Pt2+ species under reducing conditions. We found that reduction of Pt2+ species is strongly coupled with the reduction of Ce4+ cations to Ce3+ and yields sub-nanometer Pt particles. Remarkably, this process can be mediated by the interaction with any reducing agents, such as, for example, metallic Sn. The reaction involves oxidation of Sn0 to Sn2+ coupled with the reduction of Ce4+ to Ce3+ without formation of oxygen vacancies.

Redox materials chemistry at the nanoscale

2019 Spring National Meeting

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