Comparative study of supported catalyst particles by electron microscopy methods

High-resolution transmission electron microscopy, high-resolution scanning electron microscopy and high-angle annular dark-field imaging were used to study the size distribution and surface structures of Pt model catalysts on various oxide supports. The relative merits of different electron microscopy methods for catalyst research were evaluated by comparing images recorded with microscopes of different type. It was concluded that HRTEM profile imaging was the most effective technique for direct observation of microstructure, especially the surface structure of supported particles, while HRSEM and HAADF, respectively, were preferred for characterizing the surface topology of catalyst supports and the size distribution of supported particles. Using profile imaging, crystalline monolayers caused by high-temperature reduction on {111} surfaces of Pt/TiO₂ could be recorded with atomic resolution. These overlayers help explain the drop in chemisorption ability due to high-temperature reduction, a phenomenon usually referred to as strong metal-support interaction. HRSEM showed the presence of surface steps on model TiO₂ and a concentration of larger Pt particles on these steps.