Structure of highly dispersed metals and oxides: exploring the capabilities of high-resolution electron microscopy

The potential applicability of high-resolution electron microscopy (HREM), in combination with image analysis and image simulation tools, to retrieve structural information from nanometre-sized particles present in oxide-supp orted metal and oxide catalysts is analysed. Specifically, the possibilitie s and limitations of this technique to determine features such as the size! , morphology and chemical nature of the particles, their surface structure and their structural relationship with the support are considered through t he discussion of several examples, The interpretation of a series of HREM images of Pt and Ph catalysts suppor ted on cerium oxides after treatments under different redox environments il lustrates the case of highly dispersed metals. In addition, the results obt ained in this study provide an approximate picture of the evolution of meta l-support interaction effects in this family of catalysts, which is closely related to three-way catalysts (TWCs). The results of a nanostructural inv estigation of two catalyst systems, one consisting of MgO-supported neodymi a clusters and the second of vanadium-magnesium oxide also supported on MgO , provide the examples for supported oxide catalysts. These find applicatio n in oxidation reactions. For the former, the growth of neodymia in the for m of rounded patches in a parallel orientation relationship with the suppor t has been observed. For the vanadia-containing catalysts, the formation of a weakly ordered MgV2O4 spinel surface phase on the MgO support crystallit es, after exposure to typical reaction conditions in the oxidative dehydrog enation of propane, has been confirmed. The structural relationship at the spine/MgO interface has also been established. Copyright (C) 2000 John Wile y & Sons, Ltd.