Metal doping

For the alkali metal doped Cgo compounds, charge transfer of one electron per M atom to the Cgo molecule occurs, resulting in M+ ions at the tetrahedral and/or octahedral symmetry interstices of the cubic Cgo host structure. For the composition MaCgg, the resulting metallic crystal has basically the fee structure (see Fig. 2). Within this structure the alkali metal ions can sit on either tetragonal symmetry (1/4,1/4,1/4) sites, which are twice as numerous as the octahedral (l/2,0,0) sites (referenced to a simple cubic coordinate system). The electron-poor alkali metal ions tend to lie adjacent to a C=C double... 

TS-1 = metal doped zeolite Bovicelli. R Lupattelli. R Sanetti, A. Mincione, E. Tetrahedron Lett., 1994, 35, 8477... 

In the first three cycles, the capacity of the alanate is high for both materials, the titanium metal-doped and the nitride-doped material. However, after 15 cycles the hydrogen capacity decreases significantly below 4% for the titanium metal-doped sample, whereas for the nitride-doped sample the capacity remains high at about 5% hydrogen. 

Effect of the various transition metals doping on TiOj/SiOi... 

Fig 5. TCE removal efBdency with various transition metals doped on "nOj/SiCh. 

The TID design proposed Patterson consists of an alkali metal doped cerwlc cylinder, containing an embedded heater surrounded by a cylindrical collector electrode [100]. The ceramic thermionic emitter is biased at a negative potential with respect to the collector electrode, and it is heated to a surface temperature of 400-800 C, depending on the mode of detection. The response of the detector to different elements depends on the electronic work function of the thermionic surface (i.e., the... 

A. F. Carley, S. D. Jackson, J. N. O Shea and M. W. Roberts, Oxidation states at alkali-metal doped Ni(110)-O surfaces, Phys. Chem. Phys., 2001, 3, 274. 

Although the role of rare earth ions on the surface of TiC>2 or close to them is important from the point of electron exchange, still more important is the number of f-electrons present in the valence shell of a particular rare earth. As in case of transition metal doped semiconductor catalysts, which produce n-type WO3 semiconductor [133] or p-type NiO semiconductor [134] catalysts and affect the overall kinetics of the reaction, the rare earth ions with just less than half filled (f5 6) shell produce p-type semiconductor catalysts and with slightly more than half filled electronic configuration (f8 10) would act as n-type of semiconductor catalyst. Since the half filled (f7) state is most stable, ions with f5 6 electrons would accept electrons from the surface of TiC>2 and get reduced and rare earth ions with f8-9 electrons would tend to lose electrons to go to stabler electronic configuration of f7. The tendency of rare earths with f1 3 electrons would be to lose electrons and thus behave as n-type of semiconductor catalyst to attain completely vacant f°- shell state [135]. The valence electrons of rare earths are rather embedded deep into their inner shells (n-2), hence not available easily for chemical reactions, but the cavitational energy of ultrasound activates them to participate in the chemical reactions, therefore some of the unknown oxidation states (as Dy+4) may also be seen [136,137]. 

Semiconductor electrodes seem to be attractive and promising materials for carbon dioxide reduction to highly reduced products such as methanol and methane, in contrast to many metal electrodes at which formic acid or CO is the major reduction product. This potential utility of semiconductor materials is due to their band structure (especially the conduction band level, where multielectron transfer may be achieved)76 and chemical properties (e.g., C02 is well known to adsorb onto metal oxides and/ or noble metal-doped metal oxides to become more active states77-81). Recently, several reports dealing with C02 reduction at n-type semiconductors in the dark have appeared, as described below. 

The reaction of 2-propanol to propanone and propene over a series of alkali-metal-doped catalysts with use of microwave irradiation has been studied by Bond et al. [90], The nature of the carbon support was shown to affect the selectivity of the catalyst. Under microwave irradiation the threshold reaction temperature (i. e. the lowest temperature at which the reaction proceeded) was substantially reduced this was explained in terms of hot spots (Sect. 10.3.3) formed within the catalyst bed. 

Similar N2 fixation has been seen with (H20 + N2)/Ti02 and other metal-doped mineral surfaces, producing ... 

Mori M, Itoh H, Mori N, Abe T, Yamamoto O, Takeda Y, and Imanishi N. Reaction between alkaline earth metal doped lanthanum chromite and yttria stabilized zirconia In Badwal SPS, Bannister MJ, and Hannink RHJ. Science and Technology of Zirconia V. Lancaster, PA Technomic Publishing Co., 1993 776-785. 

J. Kido and T. Matsumoto, Bright organic electroluminescent devices having a metal doped electron injection layer, Appl. Phys. Lett., 73 2866-2868 (1998). 

In contrast to carbon, which forms structures derived from both sp2 and sp3 bonds, silicon is unable to form sp2 related structures. Since one out of four sp3 bonds of a given atom is pointing out of the cage, the most stable fullerene-like structure in this case is a network of connected cages. This kind of network is realized in alkali metal doped silicon clathrate (19), which were identified to have a connected fullerene-like structure (20). In these compounds, Si polyhe-dra of 12 five-fold rings and 2 or 4 more six-fold rings share faces, and form a network of hollow cage structures, which can accommodate endohedral metal atoms. Recently, the clathrate compound (Na,Ba), has been synthesized and demonstrated a transition into a superconductor at 4 K (21). The electronic structure of these compounds is drastically different from that of sp3 Si solid (22). 

Stoyanov, S.R. Titov, A.V. Krai, P., Design and Modeling of Transition Metal-doped Carbon Nanostructures. Coord. Chem. Rev. 2009, 253 2852-2871. 

Sphalerite, which is also known as Blende, is an important mineral of zinc. Most natural sphalerite contains iron more or less in lattice with the amount depending on the chemical environment and temperature (Lusk et al., 1993). High iron sphalerite is called marmatite. The studies of the electronic structure and surface properties of ZnS and transition metal doped ZnS are of interest from both a fundamental and practical perspective. As discussed in Chapter 6, sphalerite has... 

Bogdanovic, B., Brand, R.A., Marjanovie, A., Sehwikardi, M., Tolle, J. 2000. Metal doped sodium aluminum hydrides as potential new hydrogen storage materials. J Alloys Comp 302 36-58. 

Hwang, D.W., Kim, H.G., Jang, J.S., Bae, S.W., Ji, S.M., Lee, J.S. 2004. Photocatalytic decomposition of water-methanol solution over metal-doped layered perovskites under visible light irradiation. Catal Today 93-5 845-850. 

Since alkali metal doped fullerenes are conductors, and low-temperature superconductors, one wonders if the curved polynuclear hydrocarbons might exhibit a similar behavior. 

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