Surface Coverage of Carbon

FIGURE 4.3 Left The unreconstructed surface of 50% C/fccCo (100). Right The clock reconstructed surface of 50% C/fcc Co (100). The darker spheres represent cobalt atoms and the lighter ones (in the fourfold hollow sites) represent carbon atoms. (Reprinted from Ciobica. I. M.. van Santen, R. A., van Berge, P. J., and van de Loosdrecht, J., Adsorbate Induced Reconstruction of Cobalt Surfaces, Surface Science, 602, 17-28. Copyright 2008, with permission from Elsevier.) 

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However, the analysis of the data was carried out in such a way as to cast doubt on the validity of these conclusions (Vayenas54). Okamoto, Kawamura and Kudo48 went on to use the e.m.f. interpretation from the above work49 to further investigate the mechanism of CO oxidation over platinum by using the cell as a probe of the surface coverage of carbon monoxide. 

Both the propagation and the termination reaction will require a certain amount of hydrogen. In principle the coverage of hydrogen will be a function of the surface coverage of carbon containing species and the pressure of hydrogen, hence... 

Cl, acidic" carbon C2, typical as-reccived carbon C3, basic carbon, (b) Effect of pH on the /vnitrophenol surface coverage of carbons having different surface chemistry. (From Ref. 674 see al.so Fig. 32 and Section V.)... 

In Eq. (2) 6c is the surface coverage of carbon and Xb is the weight fraction of carbon in the segregation layer of Ni (g carbon/g Ni). The concentration of carbon dissolved in Ni at the support side of the particle equals the saturation concentration of filamentous carbon in Ni during steady-state carbon filament growth (CNi,r= C>at) (7, 13). 

Figure 6.8 Surface coverage of carbon at OCVs fore different operating temperatures.

As a result of assumption 4, the surface coverage of carbon monoxide is taken as 1, and the resulting expression for the surface coverage of atomic nitrogen is obtained as... 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

Figure 2.2. Thermal desorption spectra of carbon monoxide, measured mass spectrometically at mass 28 (atomic units, a.u.), on a platinum (100) surface upon which potassium has been pre-adsorbed to a surface coverage of 0K.7 Reprinted with permission from Elsevier Science.

Winslow, P., and Bell, A. T. 1985. Studies of the surface coverage of unsupported ruthenium by carbon- and hydrogen-containing adspecies during carbon monoxide hydrogenation. J. Catal. 91 142-54. 

Figure 2.9 Thermal desorption of carbon monoxide from two rhodium surfaces in ultrahigh vacuum, as measured with the experimental set-up of Fig. 2,10. Each curve corresponds to a different surface coverage of CO. At low coverages CO desorbs in a single peak indicating that all CO molecules bind in a similar configuration to the surface. At higher coverages, an additional desorption peak appears, indicative of a different adsorption geometry (courtesy of M.J.P. Hopstaken and W.E. van Gennip [141).

Before reviewing reactions of the individual hydrocarbons, some overall trends will be discussed. In general, post-reaction surface analysis by AES showed the presence of submonolayer coverages of carbon, with a fractional coverage fairly independent of reaction conditions for a given alkane. The amount of carbon left on the surface increased approximately linearly with the size of the parent hydrocarbon molecule. This carbon residue is not believed to be an important intermediate in the hydrogenolysis reactions , however,... 

In equation 5, C is amorphous carbon and CF2 changes to many perfluorocarbons, such as CF4, C2F6, etc., by secondary reactions. The surface coverage of graphite fluoride on the anode depends on the relative reaction rates of equations 4 and 5. Equation 6 has been introduced to analyze the wettability of the carbon surface with graphite fluoride formed on it.2 It shows the relationship between the fraction of effective surface for equation 3 per unit surface area of carbon (a) and the contact angle (0) of a fluorine gas bubble on the surface of the carbon electrode.2... 

Figure 5.8 Cyclic voltammograms for the Os2+/3+ redox reaction within spontaneously adsorbed [Os(OMebpy)2(p3p)Cl]+ monolayers. From right to left, the electrode materials are platinum, gold, carbon and mercury. The scan rate is 50 Vs-1, with a surface coverage of 1.0 0.1 x 10-1° mol cm-2 the supporting electrolyte is aqueous 1.0 M NaC104. Reprinted with permission from R. J. Forster, P. J. Loughman and T. E. Keyes,/. Am. Chem. Soc., 122,11948 (2000). Copyright (2000) American Chemical Society...

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