Platinum–Tin Surface Alloys Studied during O2 Exposure and CO Oxidation Using Grazing Incidence XANES

Abstract

Platinum–tin catalysts have been used industrially for decades, but their structural evolution under reaction conditions and the causes of their improved activity relative to platinum are still not well understood. In this study, we investigate Sn/Pt(111) and Sn/Pt(223) surface alloys during oxygen exposure and catalytic CO oxidation using grazing incidence X-ray absorption spectroscopy (GI-XAS). The spectra were collected in fluorescence mode, and the XANES region was used for analysis. In O₂, the Sn/Pt surface alloys segregate, and tin oxide similar to SnO₂ forms. In CO and O₂, Sn(II) oxide forms on the Sn/Pt surfaces. The spectra from the Sn(II) oxide qualitatively agree with the simulated spectra of previously studied surface oxides but not with SnO. The study provides insights into the behavior of well-defined Sn/Pt surfaces under realistic conditions and connects ambient-pressure catalysis with previous surface science research.