Transmission electron microscopy phase transformations studies

Richard et al. studied a model Pt/Al203 catalyst by transmission electron microscopy and Auger electron microscopy. Oxygen treatments under industrial catalyst regeneration conditions transform a monomodal distribution of platinum particles (mean diameter 1.8 nm) into a bimodal distribution consisting of a phase of particles 10 to 40 nm in diameter and a phase of very small clusters (diameter <1 nm). This observation of stable small clusters is direct evidence for platinum catalyst support interaction. An exchange of water between particles that operate on a molecular scale and might include platinum oxide is postulated. 

Leonard (1977) traced the transformation sequence kaolinite-metakaolinite-spinel-muUite by studying the radial electron density (RED) distribution of kaolinite and its transition products as a function of temperature, and correlated the results with chemical information obtained with X-ray fluorescence spectroscopy. While the presence of some Si-Al spinel could not completely be ruled out, most of the A1 atoms were found in the configuration of y-Al203 beyond a firing temperature of 900°C. This assumption was corroborated by Sonuparlak et al. (1987), who showed by transmission electron microscopy (TEM) in conjunction with energy-dispersive X-ray (EDX) spectroscopy that the spinel phase formed at 980 °C, indicated by a strong exothermic DTA peak, contains <10 mass% Si02, if any. 

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