Rare earth-transition metals-carbon

The basic elements of a SOFC are (1) a cathode, typically a rare earth transition metal perovskite oxide, where oxygen from air is reduced to oxide ions, which then migrate through a solid electrolyte (2) into the anode, (3) where they combine electrochemically with to produce water if hydrogen is the fuel or water and carbon dioxide if methane is used. Carbon monoxide may also be used as a fuel. The solid electrolyte is typically a yttrium or calcium stabilized zirconia fast oxide ion conductor. However, in order to achieve acceptable anion mobility, the cell must be operated at about 1000 °C. This requirement is the main drawback to SOFCs. The standard anode is a Nickel-Zirconia cermet. 

The quantitative aspect of the EXAFS technique is also well known and the literature gives several studies where chemisorption and EXAFS measurements are compared (see for example We can illustrate this particular contribution of the spectroscopy by a study of rare earth transition metal catalysts prepared from intermetallic LaNij-type compounds. The three classical preparation steps are here skipped with a carbon monoxide hydrogenation reaction. The intermetallic phase is transformed into a rare earth oxide upon which the transition metal is left as metallic clusters which form the active species. This transformation has been followed as a function of the time reaction In Fig. 5 we plot the Fourier transforms of CeNij at the nickel edge before the reaction (a), after 10 hours (b) and after 27 hours (c) under the CO + H2 mixture. These are all compared to elemental nickel (d). The increase of the amplitude of the first peak and the growth of three new ones at greater distances are the consequence of the formation of nickel particles. A careful analysis of these four shells has allowed us quantitatively to estimate the fraction of extracted nickel during the reaction as 30% after 10 hours and 80% after 27 hours on a CO + flux at 350 °C. 

Iron is the second most abundant metal and the fomth most abundant element found in Earth s crust. In 1951, Kealy and Pauson made the extraordinary discovery of ferrocene. Prior to that time, complexes containing transition metal-carbon bonds were rare, and it was thought that these bonds must be unstable. The high thermal stabihty of ferrocene changed many of these ideas, and organoiron chemistry... 

Nearly all transition metals are oxidized readily, so most ores are compounds in which the metals have positive oxidation numbers. Examples include oxides (Ti02, mtile Fc2 O3, hematite C112 O, cuprite), sulfides (ZnS, sphalerite M0S2, molybdenite), phosphates (CeP04, monazite YPO4, xenotime both found mixed with other rare earth metal phosphates), and carbonates (FeC03, siderite). Other minerals contain oxoanions (MnW04, wolframite) and even more complex stmctures such as camotite, K2 (002)2 ( 4)2 2 O ... 

According to a two-sublattice mean field model, the EMD of inter-metallic compounds is determined by the competition between the EMDs of the rare earth sublattice and the transition metal sublattice. In the Th2Zn]7-type crystal lattice, the Sm sublattice prefers c-axis anisotropy to others because of the positive Stevens factor (aj) of Sm, and the Fe sublattice contributes to the c-plane anisotropy. Both Co and carbon in Sm2(Fe1 xCox)17C>. help to enhance the contribution of the Sm sublattice dominant to the EMD, but the effect of carbon is larger than that of Co. 

From this example, it would appear that even in dimetallofullerenes, the valence levels of rare-earth encapsulants hardly hybridise at all with the carbon states, leading to integer valencies, like three, in the case of Ce2 C72. The next class of dimetallofullerenes to be dealt with are those of the transition metals, and these are quite a different story. 

In the course of IR pyrolysis, according to mass spectrometry and gas chromatography data, various gas products of destruction of PAN polymeric chain are present in the reaction chamber, including hydrocarbons such as ethylene and propylene [17, 18], These hydrocarbons provide the carbon source. Catalytic decompositions of hydrocarbons at high intensity IR-radiation in the presence of metallic Gd leads to the formation of carbon nanostructures such as observed bamboo-like CNT. It is well known that Ni, Co Fe have conventionally been used widely as metallic catalysts for high temperature pyrolysis of hydrocarbons. Recently bimetallic components was shown to be more effective than single metals as catalysts. Especially transition metals with addition of rare-earth metals such as Y, Ce, Tb, La and Ho [19]. In this work catalytic activity of single metallic Gd in the IR-pyrolysis of hydrocarbons are found by us for the first time. 

From the trend in acidities of the hydrogen halides in water, it follows that fluoride is the most basic or nucleophilic of the halides and iodide the least basic if the hydrogen ion is considered the reference acid. It should be recalled (p. 169) that this order of halide basicities is the same as that toward small, multicharged ions with rare-gas structures (for example, Be2+, A 3, and Si4+). A different, and sometimes reversed, order of basicities or nucleophilicities is observed toward certain ions of the post-transition metals (for example, Cu+, Hg +). For a number of ions (for example, Be+2, B+3 and Ta+6), fluoride complexes may exist in aqueous solution, whereas the other halo-complexes do not. Only a few of the elements having positive valence states form no halo-complexes the most important of these are carbon, the rare earths, the alkali metals, and the heavier alkaline-earth metals. 

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