The structure of Pt particles on γ-Al₂O₃ support

Samples of the catalyst Pt/γ-Al₂O₃ have been examined by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and microdiffraction techniques. An epitaxic relationship of metallic Pt crystals on the γ-Al₂O₃ has been established. In both calcined and reduced samples, the crystalline oxide α-PtO₂ was found along with metallic Pt. The oxide has a hexagonal lattice with unit-cell dimensions about 6% smaller than those previously reported. Microdiffraction from areas less than 20 Å in diameter, combined with HRTEM, STEM and secondary electron microscopy (SEM), has proved to be a very powerful technique for the study of the structures of particles less than 50 Å in size.