Cerium general properties

Enhancement by strong acids such as TFA is a general feature of oxidations with metal acetates. Metal trifluoroacetates in TFA are much more powerful oxidants (electrophiles) than the corresponding acetates in acetic acid. Activation of the metal oxidant in TFA has been observed with co-balt(III)217 249,259,27S 276 manganese(III),237,275 lead(IV),277-281 thallium-(III),282-287 cerium(IV),288 289 and copper(II).290 Similarly, the electrophilic properties of copper(I)291 and mercury(II)292 acetates are strongly enhanced by replacement of acetate by trifluoroacetate. It has been proposed217,276 that the potent oxidizing properties of Co(III) trifluoroacetate are due to ionization to the cationic Co(III) species,... 

Rare earth elements, such as yttrium, cerium and samarium, are well known to stabilize tetragonal Zr02 at lower temperatures, although the tetragonal Zr02 is generally stable at and above 1373 K. In the present study the effect of rare earth element addition on the catalytic properties of the amorphous Ni-Zr alloy-derived catalysts has been examined in order to improve the catalytic activity of the catalysts. 

It is generally held that metal oxide perovskites with extrinsic oxygen vacancies react with atmospheric water. This entrains hydrogen into the lattice and leads to their significant proton conducting properties. The location of these hydrogen atoms was studied as a function of a series of dopants in a cerium based ceramic. The dopants were niobium, holmium... 

For the two common lanthanides lanthanum and neodymium that there are no quality heat capacity measurements available between 20 and 298 K and the selected entropy values at 298 K are therefore little more than educated guesses. Further measurements are also required on alpha cerium between 20 and 96 K in order to obtain a precision value for the entropy at 298 K. What is woiryingly being shown up by these reviews is that for many of these elements, selected values in a particular region are generally based on only one set of measurements since other measurements differ so significantly that they cannot be considered. It is possible that measurements on the pure metals will become fewer and fewer as there is a concentration oti commercially exploiting the many extraordinary properties of lanthanide compounds. 

Rare-earth elements, in contrast to their historical name, are relatively abundant in the Earth s crust, and they occur in many economically viable ore deposits throughout the world with estimated worldwide reserves of 110 million tonnes. For instance, cerium (Ce), which is the most abundant rare earth, has a relative abundance of 66.5 mg/kg, similar to that of zinc, while thuhum (Tm), which is the least abundant, has a relative abundance of 0.52 mg/kg, greater than that of cadmium and silver. The abundance of lanthanides in nature shows an even-odd alteration with atomic number. As a general rule, owing to their extremely similar chemical properties, especially valences and ionic radii, geochemical processes often concentrate these elements in the same minerals, where elements are intimately mixed, and therefore they always occur in the same ore deposits. Nevertheless, owing to its smaller atomic and ionic size, scandium only occurs in rare-earth ores in minor amounts. 

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