Distinctive Kinetic Signatures of Surface Segregation Processes in Bimetallic Nanoparticle Catalysis

Surface segregation in bimetallic catalysts, driven by reaction conditions, can alter active site distributions and profoundly impact catalytic performance, yet its influence on reaction kinetics is not well understood. Using CO oxidation on bimetallic PtCu nanoparticles as a model system, we show that temperature-dependent, oxygen-induced surface segregation of Cu atoms leads to reversible changes in the concentration and coordination of the catalytically active Pt surface sites and a corresponding increase in apparent activation energy at higher temperatures. This behavior is opposite to that of pure metals, where activation energies typically decrease with the temperature. Our kinetic studies are supported by in situ infrared spectroscopy, density functional theory calculations, and microkinetic modeling. Similar kinetic trends observed in PtCo, which exhibits the surface segregation, but not in PtRu alloys, which do not change under reaction conditions, suggest that atypical variations in kinetic parameters can serve as easily accessible indicators of surface segregation. These results establish a direct link between dynamic surface restructuring and macroscopic kinetics in bimetallic systems.