REDISPERSION OF PLATINUM ON PT/AL2O3 MODEL CATALYST IN OXYGEN STUDIED BY TRANSMISSION ELECTRON-MICROSCOPY

A model Pt/Al2O3 catalyst was studied by transmission electron microscopy and Auger electron spectroscopy. O2 treatments under industrial catalyst regeneration conditions (500°C, 20 Tort, 1 h) transform a monomodal distribution of Pt particles (mean diameter 18 Å) into a bimodal distribution consisting of a phase of particles 40 to 100 Å in diameter and a phase of very small clusters (diameter < 10 Å). This observation of stable small clusters is direct evidence for a Pt catalyst dispersion in O2. Auger spectroscopy gives in situ information about particle transformation and support interaction. An exchange of matter between particles which operates on a molecular scale and might include platinum oxide is postulated. © 1990.