Potassium doping

Fig. 22. A comparison of the rate of methane synthesis over a clean single crystal Ni(100) catalyst with the corresponding rate over a potassium-doped catalyst. Total reactant pressure is 120 torr, Hj/CO = 4/1. (From Ref. 148.)...

Figure 6.25. Valence band photoemission spectra of 1 ML Ceo on a Ag(lOO) surface as a function of potassium doping. Also shown are the spectra of the clean Ag(lOO) surface and of a Ceo multilayer (bottom). All binding energies are referred to the L f of polycrystalline silver. Reprinted from Surface Science, Vols. 454-456, C. Cepek, M. Sancrotti, T. Greber and J. Osterwalder, Electronic structure of K doped Ceo monolayers on Ag(OOl), 467 71, Copyright (2000), with permission from Elsevier.

Hebard AF, Rosseinsky MJ, HaddonRC, Murphy DW, GlarumSH,PalstraTTM, Ramirez AP, Kortan AR (1991) Superconductivity at 18 K in potassium-doped Cgo- Nature 350 600-601... 

With the incorporation of other ions in the oxide superconductor, the transition temperature can be sharpened. The substitution of K+ for some Ba2+ yielded (85) a superconductor with a sharper Tc. The pressure studies on the potassium-doped Ba(Pb1 xBix)Os compounds showed a decrease in Tc as the hydrostatic pressure was increased to 15 kbar. 

Potassium-doped LB film prepared from 50 layers of fullerene (C60) and deposited on a polyethylene terephtphalate substrate Microwave absorption or low-field signal Superconductivity was observed at or below 8.1 K 121... 

The /3-pinene fraction was used as a reference to determine the isomerization activity of the supports. Results given in Table 4 show that carbon VII is particularly inert with respect to /3-pinene. This behaviour is certainly related to the high content of this carbon in potassium (0.5 wt.-%). On the contrary, the CaO impurities present in carbon V seem to increase the isomerization activity of this carbon. It is well-known that the double bond shift isomerization of hydrocarbons can proceed via carbocation intermediates (protonic catalysis) or via allylic carbanion intermediates (acido-basic or purely basic catalysis) [Ref.7]. The results obtained with potassium-doped carbons show that in /3-pinene isomerization during HDS, the protonic mechanism predominates. 

The electronic and geometric structures of poly[3-(4-octylphenyl)thiophene] (POPT) 109 (Figure 22) have been studied by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS, respectively). Thermochromic effects, and new charge-induced states generated by potassium doping, have been observed by direct UPS measurement <1996SM(76)263>. 

Centi and coworkers [84] have examined the effect of potassium doping, which was found to inhibit the P—OH Br0nsted acid sites. The lack of Br0nsted sites was thought to have two unfavorable effects on the catalyst Firstly the formation of lactones and maleic anhydride from furan was inhibited and, secondly, carbon-containing residues were strongly adsorbed onto the surface, deactivating the catalyst... 

L. Lietti, P. Forzatti. G. Ramis. G. Busca. F. Bregani. Potassium doping of vanadia/titania de-NOxing catalysts Surface characterization and reactivity study, Appl. Catal. B- -Environm. J 13 (1993). 

Y. Maruyama et ai, Observation of Metallic Conductivity and Sharp Superconducting TYansition at 19 K in Potassium-Doped FVil-leride, Ceo, Single Crystal, Chemistry Letters, 1849-1852 (1991). 

The synthesis of macroscopic amounts of C o and C70 (fullerenes) has stimuiated a variety of studies on their chemical and physical properties. We recently demonstrated that C o and C70 become conductive when doped with alkali metals. Here we describe iow-temperature studies of potassium-doped both as films and bulk samples, and demonstrate that this material becomes superconducting, Superconductivity is demonstrated by microwave, resistivity and Melssner-effect measurements. Both polycrystalline powders and thin-flim samples were studied. A thin film showed a resistance transition with an onset temperature of 16 K and essentially zero resistance near 5 K. Bulk samples showed a well-defined Meissner effect and magnetic-field-dependent microwave absorption beginning at 18 K. The onset of superconductivity at 18 K is the highest yet observed for a molecular superconductor. 

The conductivity measurements were performed on potassium-doped films of Ceo that were prepared in a one-piece all-glass version of the apparatus described previously. This reaction vessel was sealed Under a partial pressure of helium... 

To elucidate the isotope effect on superconductivity, we have studied potassium-doped K3 C(jo and samples were synthesized by heating stoichiometric amounts of solvent-free C o and Cso with K metal (3 1, K Cso) in sealed quartz tubes (10" Torr) typically, 1-2 mg of was used. The temperature was ramp from 200 to 400 C over a 1-week period during the reaction. " Kj Cjo and K3 C4o samples were prepared simultaneously in the same furnace to minimize differences due to the preparative conditions. 

Figure 4. FT-ICR mass spectra showing evidence for the production of boron and boron/potassium doped 60-ati n fuiloenes. The bottom panel shows the result of reaction with ammonia. Note that the boron-doped clusters have been titrated with ammonia, demonstrating that the boron is substituting for a carbon as part of the fullerene cage. Note also that the clusters in the top panel marked K(K C4o) and K2(K C o) are missing after reaction with ammonia in the bottom panel, demonstrating that the extra potassium atoms were on the outside, unprotected by the fullerene cage.

Claye, A.S., Nemes, N.M., Janossy, A., and Eischer, J.E. 2000. Structure and electronic properties of potassium-doped single-wall carbon nanotubes. Physical Review B Condensed Matter and Materials Physics 62, R4845-R4848. 

Figure 3. wideline spectrum of potassium doped V2O5/AI2O3 with a K/V atomic... 

In Fig. 10.18 we compare the INS spectra of oriented films of pristine /ra -polyacetylene and in the sodimn and potassium doped states. Even with poor resolution, differences are apparent between the spectra. The most striking is the gap at 80 cm that appears in the doped polymers. Molecular dynamics simulations show that the translational mode that peaks at 80 cm in the pristine sample shifts down to 64 cm in the doped samples and the mode at 160 cm shifts up to 230 cm. ... 

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