Catalysis at the Rim: A Mechanism for Low Temperature CO Oxidation over Pt3Sn

Metal alloying is commonly used as a design strategy for catalyst optimization. The mechanistic understanding of this class of systems is, however, obscured by reaction induced segregation phenomena. Herein, the case of CO oxidation over Pt3Sn is investigated using density functional theory calculations combined with ab initio thermodynamics and first-principles based microkinetic modeling. It is found that Pt3Sn segregates under typical operating conditions into SnOx and an Sn deficient metal phase. The segregation is driven both by the stability of the metal oxide and the strong bonding of CO to Pt. The catalytic consequences of a metal supported SnO2 phase are explored by comparing CO oxidation at an SnOx/Pt interface with oxidation over Pt and Pt/Pt3Sn skin models. The reaction is found to proceed with lower barriers at the interface as compared to the metal-only systems and the cocatalytic role of the SnOx rim is manifested by low temperature activity. The present work highlights the effects of reaction-induced metaloxide/metal interfaces and elucidates the role of Sn in PtSn alloys for CO oxidation reactions.