Carbon surfaces nitrogen sites

Of major interest for such processes as oxidation and compound formation are results that show several stages of atomic penetration into the substrate lattice. At metal surfaces, this appears to occur mostly with small atoms oxygen, nitrogen, carbon, as well as hydrogen. In some instances, as the coverage is increased, first an overlayer is formed (e.g. O on Ni(100)). Usually, the adatom occupies high-coordination sites such as hollow sites. On less close-packed surfaces, this site puts the adatom nearly coplanar with the surface metal atoms... 

Figure 11. Human rhinovirus 14 complexed with antiviral compound WIN 52084 (2c). The molecular surface of the protein binding site is color-coded by hydrophobicity as in Figure 2 and the bonds are color-coded by atom type carbon = white, nitrogen = blue, oxygen = red, sulfur = yellow.

Another interesting process is the conversion of 1,2-dichloroethane into vinyl chloride, which was shown to be catalyzed by PAN-ACFs at 573 K [215]. The results obtained with a variety of PAN-ACFs suggest that a base-catalyzed reaction occurs on pyridinic nitrogen sites, while a radical reaction is promoted on vacant sites on the ACF surface. The HCI produced deactivates the basic sites, while vinyl chloride polymerization and carbonization leads to coking and deactivation, as shown in Figure 6.14. 

Many authors correlated the SO2 adsorption capacity with the basic centers on the carbon surface [107,108,116,118-120]. However, it has been pointed out that more SO2 was adsorbed than corresponded to the basic centers [102]. This is not surprising since the surface basic sites are quite weak, and SO2 is not a strong acid. Also, no good correlation of SO2 conversion per square meter of surface or nitrogen content was found. The correlation was much better with the N-6 content [108]. It was also reported that the SO2 oxidation capacity increased with increasing N-6 and N-Q contents [118-121]. 

The variation of activity for these catalysts, all made under the same experimental conditions, except for the carbon support, was stunning and is presented as fuel cell polarization curves in Figure 3.25. On the one hand, the specific area of all these catalysts was measured and no correlation with the catalytic activity was found. On the other hand, there was a definite correlation between the catalytic activity and the surface nitrogen concentration measured by XPS. This correlation is illustrated in Figure 3.26. It is obvious that the catalytic activity for ORR increases when the surface of the catalyst is richer in nitrogen atoms. This is a logical result, since the precursor of the Fe-N2/C catalytic site (the most... 

Fig. 2.3 Theoretical models for a N-doped carbon surface and b pure carbon surface red ball oxygen atom blue ball nitrogen atom gray ball carbon atom small gray ball hydrogen atom), c Hydrogen bond energies at different adsorption sites. Reproduced from Ref. [6] by permission of The Royal Society of Chemistry...

Gases such as Nj, Oj, NH3, COj, Hj, HjO, carbon monoxide, nitrogen dioxide, and nitric oxide are thought to be reactive in plasmas. The mechanism of their action is the same as for nonreactive gases—the surface is bombarded with ionized plasma components to generate radical sites. These subsequently react with gas molecules, creating various functionalities, depending on the plasma conditions. 

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