Cerium oxide electronic structure models

Fig. 7.4 High-resolution transmission electron microscopy (TEM) image of a rhodium on a modified cerium oxide (Ceo.gTbo.202 x) after reduction, showing how the metal is almost epitaxially attached to the support, (a) TEM image (b,c) digital diffraction patterns obtained by Fourier transformation from the images (d) structure model ...

With a few exceptions, most research applying the surface science approach to study ceria based systems has been performed in about the last five years. As evidence for this statement consider that in a 1995 book which presents a comprehesive review of surface science of oxide surfaces only a single reference to cerium oxide surfaces is cited or that in a 1997 review of structural, electronic and chemisorptive properties of metal films and particles on oxide surfaces there are six references to ceria surfaces or that in a 1998 review of surface studies of supported model catalysts there are only six references to ceria as a support. The... 

Branda MM, Loschen C, Neyman KM, lUas F Atomic and electronic structure of cerium oxide stepped model sur ces, J Phys Chem C 112(45) 17643-17651, 2008. 

Cerium tetrafluoride is the only lanthanide halide which contains a metal atom in the highest oxidation state and which is significantly volatile. An earlier study of its structure had ruled out a tetrahedral model on the basis of the amplitudes of vibration, and it was thought that it must be distorted to Czv or C3V symmetry. Now that the vibrational frequencies have been observed for the molecule isolated in rare gas matrices, it has been possible to reinterpret the electron diffraction data, using the observed frequencies in the analysis." It has been shown that the data do indeed correspond to a tetrahedral structure for the Cep4 molecule. Using four observed vibrational frequencies and the diffraction data it was possible to refine five force constants and the Ce-F distance. The value is 200.9(5) pm, corresponding to 203.6(5) pm for the distance. This is substantially shorter than the distance rf) of 218 pm in cerium trifluoride. 

In view of the above discrepancies and our interest in the oxidation of alcoholic macromolecules in acidic solutions by either multi-equivalent oxidants such as chromium (VI] [69-71] and permanganate [61-67] or one-equivalent oxidants such as hexacyanoferrate (111] [72] and cerium (IV] [73], the present work explores the nature of electron transfer and transition state in the rate-determining step as well as the influence of homogeneous catalysis and model structure of the oxidant on the kinetics of oxidation by chromic acid in acidic solutions. Furthermore, this work includes pertinent discussion with a great deal of emphasis on the oxidation mechanisms and the chemistry of interaction of such macromolecules in aqueous solutions in order to compensate such lack of information of the nature of transfer of electrons and transition states in the rate-determining step in the oxidation of macromolecules containing alcoholic groups such as polysaccharides by chromic acid. Moreover, it is of interest to... 

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