Atmosphere-Dependent Structures of Pt-Mn Bimetallic Catalysts

Pt-Mn bimetallic catalysts exhibit high activity in many heterogeneous catalytic and electrocatalytic reactions. However, the surface structure of Pt-Mn catalysts under different reaction conditions remains less explored. This work describes the construction of different surface structures of the Mn/Pt(111) model system via controlling atmospheres at variable temperatures. Our results suggest that the Pt-Mn surface alloy and nearsurface alloy can be obtained upon low-temperature and high-temperature annealing in ultrahigh vacuum, respectively. With high-temperature oxidation, near-surface Mn atoms under the Pt-skin surface segregate outwards to form MnO on the Pt(111) surface. Structural transformation between MnO/Pt(111) and Pt-Mn near-surface alloy can be repeated by alternate hightemperature oxidative and reductive treatments. CO adsorption sites change from Mn sites to Pt sites with the surface structure transformed from Mn/Pt(111) to Pt-Mn surface alloy. CO vibrational peaks shift to lower wavenumbers when the surface structure changes from Pt-Mn surface alloy to near-surface alloy. CO desorbs more easily on the surfaces of Pt-Mn surface alloy and Pt-Mn near-surface alloy compared with the clean Pt(111) surface because of the downshift of d-band center of surface Pt atoms. The feasible modulation of Pt-Mn surface structure provides a guidance for the rational design of Pt-Mn bimetallic catalysts.