Understanding the Role of Electronic Effects in CO on the Pt–Sn Alloy Surface via Band Structure Measurements

Abstract

Using angle-resolved photoemission spectroscopy, we show direct evidence for charge transfer between adsorbed molecules and metal substrates, i.e., chemisorption of CO on Pt(111) and Pt–Sn/Pt(111) 2 × 2 surfaces. The observed band structures show a unique signature of charge transfer as CO atoms are adsorbed, revealing the roles of specific orbital characters participating in the chemisorption process. As the coverage of CO increases, the degree of charge transfer between CO and Pt shows a clear difference to that of Pt–Sn. With comparison to density functional theory calculation results, the observed distinct features in the band structure are interpreted as back-donation bonding states formed between the Pt molecular orbital and the 2π orbital of CO. Furthermore, the change in the surface charge concentration, measured from the Fermi surface area, shows that the Pt surface has a larger charge concentration change than the Pt–Sn surface upon CO adsorption. The differences between Pt and Pt–Sn surfaces are due to the effect of Pt–Sn intermetallic bonding on the interaction of CO with the surface.

Size-Dependent Structures and Catalytic Properties of Supported Bimetallic PtSn Catalysts for Propane Dehydrogenation Reaction

“…As shown in Table S11, the PtSn/MFI-600H 2 sample exhibits a reasonable number of exposed Pt sites, while the PtSn/Beta-600H 2 and PtSn/SiO 2 -600H 2 samples show a very low number of exposed sites, which is largely departed from the size distributions (∼0.9 nm for PtSn/Beta-600H 2 and ∼1.6 nm for PtSn/SiO 2 -600H 2 ) according to the electron microscopy and spectroscopy characterization results. The underestimated exposed Pt sites in the PtSn/Beta-600H 2 and PtSn/SiO 2 -600H 2 samples measured by CO chemisorption could be associated with the hindered CO adsorption on bimetallic PtSn nanoparticles/nanoclusters caused by the modification of the electronic properties of Pt by Pt–Sn bonding. ,− In this sense, we think it is appropriate to compare the catalytic performances by the initial reaction rates normalized to the total Pt mass in the catalyst (a meaningful criterion for practical applications) or the exposed metal sites derived from average particle sizes to avoid the large deviation in CO chemisorption measurement. As shown in Figure S30, the PtSn/MFI-600H 2 sample exhibits the highest specific activity than the other two PtSn samples, regardless of the calculation methods.…”

Platinum-Tin Anode for Direct Sugarcane Juice Fuel Cell, a Viable Alternative for Bioenergy Systems: Clean Energy without Production of Vinasse

“…The most active composition was Pt 90 Sn 10 /C with MPD of 8.7 mW cm − 2 followed byPt 80 Sn 20 /C (4.5 mW cm − 2 ), Pt 70 Sn 30 /C (4.2 mW cm − 2 ), Pt 60 Sn 40 /C (4.0 mW cm − 2 ), Pt 50 Sn 50 /C (3.6 mW cm − 2 ), and Pt/C (0.97 mW cm − 2 ). This effect can be attributed both to the electronic properties differentiated by the insertion of tin into the Pt crystal lattice [27] and by the activation of water at less positive potentials (bifunctional mechanism), thereby removing strongly adsorbed species [28], both effects commonly attributed to PtSn combination. For all materials, only fructose and glucose peaks were noted in the chromatograms, indicating that sucrose had broken down into a fructose and sucrose molecule.…”

Surface Anion Promotes Pt Electrocatalysts with High CO Tolerance in Fuel-Cell Performance

“…Therefore, the downshift or upshift of the Pt d-band had little influence on 5σ orbitals. The CO adsorption energy is determined by the interaction between the 2π* orbitals and Pt d-band center. , It is well known that the electron donation from M (heteroatoms) to Pt results in a downshift of the Pt d-band center. Conversely, electron donation from Pt to M causes an upshift of the d-band center .…”