Lanthanides, intermetallics

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

Methanol synthesis activity of selected copper-lanthanide intermetallic catalysts (Owen et al. 1987)... 

Cubic laves phase lanthanide intermetallic compounds RM2)... 

Survey of the studies of intersublattice exchange interactions in lanthanide intermetallics... 

Fig. 18. as a function of the 3d-magnetic moment for a number of lanthanide intermetallics. Data reported for Dy2(CO -jNi,)i7 (triangles) are included. After Due (1993a). 

The HFFP method is flee of any assumptions regarding the R-R interaction. However, because of the rather large difference of Mr-Mt in almost all the lanthanide intermetallics, it can be applied for the substituted alloys only. When R is replaced by Y, the 4d electrons are introduced to the system. Thus, besides the 3d-5d hybridization, one should taken into account the influence of the 3d-4d mixing on the magnetic behaviour. For the HFFP studies, the Y substitution is applied when Mr is larger than Mj. As consequence, in the Fe, Co compounds, this magnetic dilution appears only in the R-rich ones, whereas it is applied to all of the R-Ni systems. 

Lm absorption in lanthanide intermetallics with ThCr2Si2 structure... 

Mossbauer effect methods have received wide application to the study of intermetallic compounds. This subject was first reviewed by Nowik (1966) and more recently by Taylor (1971) and also Wallace (1973) as part of general reviews of the properties of lanthanide intermetallics. Many examples are also included in the NGR review by Ofer et al. (1%8) as well as in the text by Greenwood and Gibb (1971). 

Resumd of nuclear gamma resonance measurements on lanthanide nuclei in the magnetically ordered state of lanthanide intermetallic compounds. 

Detection of such resonances in lanthanide intermetallics was first reported by Jones (1967) on Pr in PrP and PrAs, and on m in TmP, TmAs, and TmSb, all of which have the cubic NaCI structure. Of all the lanthanide nuclei, only m has spin i hence quadrupolar complications are completely absent, and its NMR spectrum is determined entirely by the magnetic hyperfine interaction. In the case of "Pr, which has a small quadmpole moment (table 18.1), the cubic environment is helpful in reducing the quadrupolar complications in the spectrum. Resonances have also been reported for Pr in PrSe and for m in TmSe and TmAb [Jones (1968)]. All of these studies are briefly summarized in table 18.14. 

The large and well-defined range of isomer shifts observed for the NGR of Eu in the di- and trivalent states of the europium ion make this isotope particularly valuable for the study of intermediate valency states in lanthanide intermetallics. Such intermediate valency states have their origin in interconfiguration fluctuations (ICF s). In the case of europium intermetallics, the unusual isomer shifts observed are interpreted in terms of fast fluctuations, on the order of 10 " sec, of an electron between a localized 4f level and the conduction band, resulting in a fluctuating charge density at the Eu nuclei. 

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