Cerium oxide computations

In Figure 8 we have plotted the lanthanum oxide, cerium oxide, and thorium oxide concentrations for sherds excavated in the Dominican Republic and Venezuela and sherds from the Metro excavations using a computer system developed for this purpose at Brookhaven National Laboratory (8). On the basis of these three oxides there is a distinct separation between the sherds from the Dominican Republic and Venezuela and those from Mexico City. Unlike the sherds from the Dominican Republic and Venezuela, the sherds from Mexico City appear not to have originated in Spain, at least at that specific source. There is further evidence of this distinction between the two sets of sherds. X-ray diffraction analysis of the samples from Jerez and from the New World showed that the sherds from Jerez, the Dominican Republic, and Venezuela had intense quartz peaks whereas the sherds from Mexico City did not. This constitutes additional evidence that the majolica from Mexico City came from a different source than the majolica from the Caribbean sites. 

Figure 8. Computer projection of three-dimensional plot of cerium, lanthanum, and thorium oxide concentrations for Spanish Colonial majolica sherds. The data divides into a group having its source in Spain and a group whose source is Mexican, as discussed in the text.

The use of CeOs-based materials in catalysis has attracted considerable attention in recent years, particularly in applications like environmental catalysis, where ceria has shown great potential. This book critically reviews the most recent advances in the field, with the focus on both fundamental and applied issues. The first few chapters cover structural and chemical properties of ceria and related materials, i.e. phase stability, reduction behaviour, synthesis, interaction with probe molecules (CO. O2, NO), and metal-support interaction — all presented from the viewpoint of catalytic applications. The use of computational techniques and ceria surfaces and films for model catalytic studies are also reviewed. The second part of the book provides a critical evaluation of the role of ceria in the most important catalytic processes three-way catalysis, catalytic wet oxidation and fluid catalytic cracking. Other topics include oxidation-combustion catalysts, electrocatalysis and the use of cerium catalysts/additives in diesel soot abatement technology. 

As mentioned in the introduction, the ability of cerium to switch between the -f 4 and -1-3 oxidation states determines many important applications of ceria-based materials. For this reason, the energy change associated with the C e +/C e + bulk reduction in different environments has been investigated using computer simulation techniques. 

Lutetium is also a very rare metal, with a world production (as lutetium oxide) of approximately 10 tons per year. One commercial application is known it is used as a P-emitter, (when Lu-176 has been exposed to neutron activation) in the oil refining industry (Emsley 2001). It was used in so-called-bubble memory, a technology for computer memory that has become obsolete, since hard disks have made their rapid substantial advance. It is still used in scintillation crystals for PET-scanners (positron emission scanners). It is used here in the form of cerium-doped Lutetium oxy-orthosilicate (LSO), with the formula Ce2x Lu2(l — x) SiOs, where x is within tire range from approximately 2 x 10 to approximately 3 X 10 (Melcher 1990 Daghighian et al. 1993). 

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