AVS 66th International Symposium & Exhibition
    Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Thursday Sessions
       Session HC+2D+SS-ThM

Paper HC+2D+SS-ThM12
Cooperativity Between Pd and AgOx Phases on Ag(111)

Thursday, October 24, 2019, 11:40 am, Room A213

Session: Nanoscale Surface Structure in Heterogeneously-Catalyzed Reactions
Presenter: Jason Weaver, University of Florida
Authors: V. Mehar, University of Florida
M. Yu, University of Florida
J.F. Weaver, University of Florida
Correspondent: Click to Email
Metals dispersed on a reactive metal-oxide have potential to effect selective 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 oxidized Ag(111) as well as Pd/AgOx surfaces that are generated by depositing metallic Pd onto a single-layer AgOx structure in ultrahigh vacuum (UHV). Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) show that the oxidation of Ag(111) with atomic oxygen mainly produces a single-layer AgOx phase with a p(4 x 5r3) structure as well as smaller amounts of p(4 x 4) and c(3 x 5r3) structures during the initial stages of oxidation. Surface infrared spectroscopy and temperature programmed reaction spectroscopy (TPRS) demonstrate that the single-layer AgOx structures are nearly unreactive and bind CO negligibly at temperatures down to ~100 K. In contrast, we find that CO adsorbs and oxidizes efficiently on Pd islands during TPRS, even when the AgOx phase is the only oxidant source. STM further demonstrates that the metallic Pd islands induce partial reduction of the AgOx support structure at 300 K. We find that the Pd/AgOx surfaces continue to exhibit high CO oxidation activity with increasing Pd coverage up to nearly 2 ML (monolayer), suggesting that oxygen transfer from the AgOx phase occurs at both the interior and perimeter of Pd islands. Our results reveal a cooperative mechanism for CO oxidation on Pd/AgOx surfaces wherein O-atoms from the AgOx support phase migrate onto metallic Pd islands and react with adsorbed CO to produce CO2. These findings illustrate 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 (AgOx) support.