Core-Shell Phase Separation and Structural Transformation of Pt3Sn Alloy Nanoparticles Supported on γ-Al2O3 in the Reduction and Oxidation Processes Characterized by In Situ Time-Resolved XAFS

Unique catalytic capabilities of supported bimetallic nanoparticles with synergistic functions mark them as a significant advancement in catalytic technologies. The dynamic behavior and kinetics of structural change of catalysts in the reduction and oxidation processes are fundamental issues to understand their catalytic properties and performances as well as to regulate the structure and composition in alloy nanoparticles. The core-shell phase separation and structural transformation of Pt3Sn alloy nanoparticles on gamma-Al2O3 during the reduction and oxidation processes were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticle catalyst. The oxidation of Pt3Sn nanoparticles on gamma-Al2O3 with O-2 at 673 K proceeded by three successive steps via two intermediates to form NO core nanoparticles with SnO2 shells, whereas the reduction of the oxidized nanoparticles with H-2 at 673 K proceeded as a single process with similar rate constants at Pt and Sit sites. The kinetic parameters and mechanisms for the reduction and oxidation of the Pt3Sn/gamma-Al2O3 catalyst were determined by the time-resolved XAFS techniques.