Nanoscopic observation of strong chemical interaction between Pt and tin oxide

Platinum catalysts supported on tin oxide were prepared by the impregnation method and were treated in several conditions. The change of their structure by the treatment was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. In the as-prepared catalyst, platinum particles with their mean size of ca. 3 nm were highly dispersed on SnO2 supports. After the treatment in reduction atmosphere, the intermetallic compounds ascribed to PtSn and Pt3Sn were formed, and the growth of particle by aggregation was observed. Moreover, the particles with core - shell nanostructure were observed in the catalyst reduced at higher temperatures. It was revealed that the core - shell structure was formed by the phase separation of Sn species from the intermetallic compound particles when the catalyst was treated by mild reoxidation such as exposure to air. On the other hand, after the reoxidation treatment, the mean particle size of the metal particle became smaller and crystallized in the unique particle morphology. After reoxidation at higher temperatures, the intermetallic compounds disappeared, and morphology of platinum particles observed in the as-prepared catalyst was regenerated. These structural changes in the interface between platinum and SnO2 should be related to the unusual CO adsorptive property of Pt/SnO2.