Synchrotron-based ambient pressure X-ray photoelectron spectroscopy (APXPS) experiments have been employed to elucidate the dynamic behavior of dilute PdAg bimetallic catalysts. The experiments were performed at the ALS facility in Lawrence Berkeley Laboratory and the NSLS-II facility at Brookhaven National Laboratory. Model APXPS and scanning tunneling microscopy (STM) experiments indicate a Ag-Pd-Ag sandwich structure for submonolayer coverages of as-deposited Pd/Ag(111) at 300 K. Oxidation in 2 Torr of O2 induces significant structural reorganization of the PdAg interface that is stable in ultra-high vaccum (UHV) conditions. Incremental reduction of the Pd/Ag oxide with increasing pressures of reducing gases (H2 and CO) exhibits behavior distinct from either oxidized Pd(111) or Ag(111). APXPS experiments suggest that the unique reduction behavior of the PdAg interface originates from the spillover of surface intermediates from Pd to Ag, as demonstrated by H2, and Ag to Pd, as demonstrated by CO. The spillover of these intermediates has strong implications towards tuning the reactivity and selectivity of the dilute PdAg system. This study demonstrates the importance of model APXPS studies in understanding the dynamic behavior of complex bimetallic catalyst systems.

Ambient pressure XPS for catalysis studies of binary alloys

256th National Meeting (2018)

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