Surface Studies of Catalytic Cerias Using Atomic Resolution TEM

Available from UMI in association with The British Library. Requires signed TDF. There have been recent developments in a number of techniques allowing detailed structural and analytical information about supported metal catalysts to be obtained. In this study the atomic level capability of the high resolution electron microscope has been exploited to characterise the surface of oxide and metal/oxide systems. Two morphologically different cerias in a form suitable for use in catalysis have been prepared. These cerias have been impregnated with respectively small platinum and gold particles to create real and model metal/ceria catalyst systems. The cerias and metallised cerias have been characterised using the high resolution transmission electron microscopical technique of surface profile imaging as well as other more common catalyst characterisation techniques such as chemisorption, porosimetry and X-ray diffraction. Electron-beam induced rearrangements on the surface of ceria on the atomic scale have been observed. Shape changes in small metal particles have been noted including the observation of epitaxial alignment with the ceria surface. Metal particles have been induced to spread themselves on the oxide surface forming monolayers which can be distinguished from the substrate. Structural defects found in certain ceria preparations have been identified as being octahedral in shape and existing as pores on the surface as well as voids in the crystal interiors. Metal-support interaction of platinum on ceria has been investigated using temperature programmed reduction, controlled environment TEM and microreactor experiments involving transfer without exposure to air to a high resolution electron microscope. Although a metal-support interaction after high temperature reduction was not identified there was evidence for another type of interaction which rendered the platinum unavailable for hydrogen chemisorption after reduction at 200^circC. No physical occurrence could be identified to account for this and the availability for hydrogen adsorption after reduction at 400^circC. Real ceria and plantinised ceria catalysts have been compared in reactions of ethylene oxidation, self hydrogenation and hydrogenation and methyl cyclopentane hydrogenolysis. Surface profile imaging has been used to characterise the catalysts after use.