Reversible structural transformation of FeOx nanostructures on Pt under cycling redox conditions and its effect on oxidation catalysis

Understanding dynamic changes of catalytically active nanostructures under reaction conditions is a pivotal challenge in catalysis research, which has been extensively addressed in metal nanoparticles but is less explored in supported oxide nanocatalysts. Here, structural changes of iron oxide (FeOx) nanostructures supported on Pt in a gaseous environment were examined by scanning tunneling microscopy, ambient pressure X-ray photoelectron spectroscopy, and in situ X-ray absorption spectroscopy using both model systems and real catalysts. O-Fe (FeO) bilayer nanostructures can be stabilized on Pt surfaces in reductive environments such as vacuum conditions and H-2-rich reaction gas, which are highly active for low temperature CO oxidation. In contrast, exposure to H-2-free oxidative gases produces a less active O-Fe-O (FeO2) trilayer structure. Reversible transformation between the FeO bilayer and FeO2 trilayer structures can be achieved under alternating reduction and oxidation conditions, leading to oscillation in the catalytic oxidation performance.