Metals dispersed on a reactive metal-oxide have potential to effect oxidation catalysis through cooperative interactions between the co-existing metal and metal-oxide phases. In this talk, I will discuss our recent investigations of the structure and reactivity of Pd/AgOx surfaces that are generated by depositing metallic Pd onto a single-layer AgOx/Ag(111) structure in ultrahigh vacuum (UHV). Scanning tunneling microscopy shows that Pd initially forms well-dispersed clusters on the AgOx layer that continue to wet the surface with increasing Pd coverage at 300 K, until transforming into a nearly conformal Pd bi-layer. We find that the pure AgOx single-layer exhibits limited CO oxidation activity during temperature programmed reaction spectroscopy (TPRS), whereas the Pd-AgOx/Ag(111) surfaces oxidize CO efficiently during TPRS. Our results demonstrate that the Pd and AgOx phases act cooperatively during CO oxidation such that the AgOx layer supplies O-atoms to Pd domains while the O-atoms efficiently react with adsorbed CO on Pd. We present experimental evidence of two processes by which O-atoms move to the Pd surfaces, namely, diffusion through the Pd domains that initiates from the buried Pd-AgOx interface and diffusion of O-atoms across the AgOx surface to the perimeters of Pd domains. Our results demonstrate generally that oxygen transport across metal/metal-oxide interfaces can be highly efficient when the oxygen chemical potential is lower on the initial metal phase (Pd) compared with the metal-oxide support (AgOx) and provide insights for understanding the mechanisms of oxygen interchange between metal and metal-oxide phases during CO oxidation.

Growth and reactivity of Pd deposits on single-layer AgOx/Ag(111)

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.