Alkali graphite intercalation compounds

Watanabe K, Knodow T, Soma M, Onishi T, Tamaru K (1973) Molecular-sieve type sorption on alkali graphite intercalation compounds. Proc. Roy. Soc. Lond. A. A333 51-67... 

Solin SA, Caswell N (1981) Raman-scattering from alkali graphite-intercalation compounds. J Raman Spectrosc 10(1) 129-135... 

We report results of first-principles molecular orbital calculations on model clusters of graphite (C24), alkali graphite intercalation compounds (MC48 M = Li, Na, K, Rb, Cs), fullerene (Ceo), and fluorinated fullerenes (CeoFa, x — 18, 36, 48). The calculated partial densities of states (pDOS) are compared with measured x-ray absorption near edge structure (XANES) spectra, x-ray photoelectron spectra (XPS), x-ray emission spectra (XES), and ultraviolet photoelectron spectra (UPS). In the case of graphite and its compounds, the calculated pDOS well reproduce features of the observed XANES and UPS spectra. The calculated pDOS and the observed XPS, UPS and XANES of CeoFx (x = 0, 36, 48) are also in satisfactory accordance. 

Carbon atoms crystallize in several forms. Graphite and diamond are well known carbon polymorphs. Fullerenes, which were discovered in the 1980 s, have also been well characterized. Carbon materials show a variety of different physical and chemical properties. Because of this the electronic structure of carbon materials has been investigated using a number of different experimental techniques, for example, XPS, UPS and XANES. Theoretical studies of carbon materials have been also performed. However, experimentally observed spectra are not always consistent with theoretical predictions. Recently, in order to understand the various kinds of observed electronic spectra, DV-Xa calculations have been performed on a small cluster model. [1] In the present paper, we report results of DV-Xa calculations performed on the carbon materials graphite, alkali graphite intercalation compounds (GIC), fullerene, and fluorinated fullerenes. 

Cj(K prepared — the first alkali metal-graphite intercalation compound. 

Figure 8.16 Layer-plane sequence along the c-axis for graphite in various stage I -5 of alkali-metal graphite intercalation compounds. Comparison with Fig. 8.15 shows that the horizontal planes are being viewed diagonally across the figure. /,. is the interlayer repeat distance along the c-axis.

In alkali metal intercalation compounds, the guest is ionised in the host, donating its outer s electron to the host s electronic energy levels. Thus there are two aspects to consider, the sites where the ion resides, and the energy levels or bands that the electron occupies. Guests such as water that remain neutral will only be discussed in the section on cointercalation. In some hosts, notably graphite, some guests accept electrons from the... 

Alkali, Alkaline Earth, and Rare Earth Metal Graphite Intercalation Compounds... 

Posternak, M., A. Balderschi, A. J. Freeman, and E. Wimmer. 1983. Prediction of electronic interlayer states in graphite and reinterpretation of alkali bands in graphite intercalation compounds. Phys. Rev. Lett. 50 761-764. 

Alstrom, P. 1986. Electronic properties of first-stage heavy alkali metal graphite intercalation compounds. Synth. Metals 15 311-322. 

Saito, M. and A. Oshiyama. 1986. Self-consistent band structures of first-stage alkali-metal graphite intercalation compounds. J. Phys. Soc. Jpn. 55 4341-4348. 

Gunasekara, N., T. Takahashi, F. Maeda, T. Sagawa, and H. Suematsu. 1988. Angle-resolved ultraviolet photoemission study of first stage alkali-metal graphite intercalation compounds. Z. Phys. B 70 349-355. 

The reaction of various carbonaceous materials with steam to yield CO, CO2, and H2 has been intensively studied. Of special interest has been the catalysis of this reaction by various alkali metal containing compounds, most notably potassium carbonate (32-37). Various mechanisms have been proposed, some including alkali metal atoms (37) or even graphite intercalation compounds (38) as intermediates. 

Table 3 Graphite-alkali metal intercalation compounds...

Graphite intercalate compounds have also been used to catalyse Fischer-Tropsch reactions. Although alkah-metal intercalates are active,the yield of hydrocarbons can be markedly improved by replacing the alkali metal with a transition-metal chloride complex or an alkali-metal/transition-metal chloride intercalate. 

W.J. Stead, I.P. Jackson, J.McCaf ey J.W. White (1988). J. Chem. Soc, Faraday Trans. II, 1988, 84, 1669-1682 Tuimelling of hydrogen in alkali-metal-graphite intercalation compounds. A systematic study of C24Rb(H2)x and its structural consequences. 

The endohedral metallofullarenes just described (and the alkali metal fullerides described on p. 285) are all formally examples of metal carbides, M cCy, but they have entirely different structure motifs and properties from the classical metal carbides and the more recently discovered metallacarbohedrenes (metcars) on the one hand (both to be considered in Section 8.4) and the graphite intercalation compounds to be discussed in Section 8.3. Before that, however, we must complete this present section on the various forms of the element carbon by describing and comparing the chemical properties of the two most familiar forms of the element, diamond and graphite. 

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