Interaction of CO with PtxAg1-x/Pt(111) surface alloys: More than dilution by Ag atoms

• Published in: Surface science 2016-08, Vol.650, p.237-254
• Main Authors: Schüttler, K.M., Mancera, L.A., Diemant, T., Groß, A., Behm, R.J.
• Format: Article
• Language: English
• Subjects: Bimetallic surface; Carbon monoxide; Chemisorption; DFT calculations; IR spectroscopy; Temperature programmed desorption
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2015.12.022

We have investigated CO adsorption on structurally well-defined PtxAg1-x/Pt(111) surface alloys, combining temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS) as well as density functional theory (DFT) based calculations. This is part of a systematic approach including previous studies of CO adsorption on closely related Pt(111)- and Pd(111)-based surface alloys. Following changes in the adsorption properties with increasing Ag content and correlating them with structural changes allow us to assign desorption features to specific adsorption sites/ensembles identified in previous scanning tunneling microscopy (STM) measurements, and thus to identify and separate contributions from different effects such as geometric ensemble effects and electronic ligand/strain effects. DFT calculations give further insight into the nature of the metal–CO bond on these bimetallic sites. Most prominently, the growth of a new CO desorption feature at higher temperature (~550K) in the TPD spectra of Ag-rich surface alloys, which is unique for the group of Pt(111)- and Pd(111)-based surface alloys, is attributed to CO adsorption on Pt atoms surrounded by a Ag-rich neighborhood. Adsorption on these sites manifests in an IR band down-shifted to significantly lower wave number. Systematic comparison of the present results with previous findings for CO adsorption on the related Pt(111)- and Pd(111)-based surface alloys gains a detailed insight into general trends in the adsorption behavior of bimetallic surfaces. [Display omitted] •CO adsorption was used to determine the chemical properties of PtAg/Pt(111) surface alloys.•CO TPD and IRRAS were used for characterization in UHV, accompanied by DFT calculations.•Experiment and calculations reveal stabilization of CO/Pt sites with Ag-rich neighborhood.•An additional desorption feature appearing at higher temperature was observed.•Comparison with similar systems (PtAu, PdAg, PdAu) underlines unique behavior of PtAg.