Reversible structural modulation of Fe-Pt(111) bimetallic surface between the surface FeO and the subsurface Fe

Using Fe-Pt(111) model catalysts, we show that surface structure of the bimetallic Fe-Pt(111) catalysts can be modulated reversibly by cycled oxidation (1.1  10-6 mbar O2, 800 K) and reduction treatments (1.1  10-6 mbar H2, 850 K) [1]. Atomically resolved STM images indicate the presence of monolayer FeO structure on Pt(111) upon each oxidation and formation of Pt-skin structure in case of reduction. XPS and ISS Fe and Pt signal intensity shows well-defined up-down oscillations with the cycle of oxidation and reduction. The dynamic behaviours at Fe-Pt(111) surface can be attributed to two opposite gas-driven mass transport processes. The surface segregation of Pt happens upon annealing in reductive atmosphere due to minimization of the surface strain energy. However, oxidation results in the outward diffusion of Fe and covering the Pt(111) surface with monolayer FeO, which is driven by the lower surface energy of metal oxides and strong interaction between oxides and Pt [2]. More importantly, the reversible structural changes have been observed in the supported Pt-based bimetallic nanoparticles, including PtFe, PtNi, PtCo, and PtCu systems deposited on HOPG [3]. The tunability of the surface structure of bimetallic catalysts may open an effective way to design highly efficient catalysts for many important catalytic processes.