Dynamics of Surface Alloys: Rearrangement of Pd/Ag(111) Induced by CO and O2

• DOI: 10.1021/acs.jpcc.8b08849
• Publication Date: 2018-11-19T21:14:47Z
• Authors: Matthijs A. van S...; Kaining Daunmu; Christopher R. O’...; Tobias Egle; Heath Kersell; Judit Oliver-Mese...; Miquel B. Salmeron; Robert J. Madix; Philippe Sautet; Cynthia M. Friend
• Keywords: Torr

Alloys of Ag and small amounts Pd are promising as bifunctional catalysts, potentially combining the inherent selectivity noble with that more reactive Pd. Stable PdAg surface alloys prepared via evaporation onto Ag(111) at room temperature followed by annealing 400 K to create a model system. Using this procedure, most stable form alloy under vacuum was determined be Ag-capped alloy, on basis combination X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), density functional theory (DFT). Extensive roughening apparent in STM images, characterized islands Ag/PdAg/Ag(111) several layers thickness. The is attributed transport from into islands. Within these islands, there driving force for dispersed, surrounded Ag, DFT modeling. Exposure CO (0.5 Torr) 300 induces migration surface, driven energetic stabilization Pd–CO bond based ambient-pressure XPS. Once drawn higher pressures temperature, it remains even very low partial temperatures below, DFT-modeled phase behavior. 1 Torr O2 also causes resurface, resulting structure persists below K. These results establish state catalyst depends strongly pretreatment operational conditions. Hence, exposure an or moderate can lead activation bringing surface. Furthermore, demonstrate which often used proxy evaluating coordination sites available catalyst, changes structure. Therefore, vibrational frequencies measured diffuse-reflectance infrared Fourier-transform (DRIFTS) materials do not necessarily provide information about their working state, fundamental understanding CO-PdAg crucial.