Carbon surface functionality

A systematic study of differently supported Ru catalysts showed that carbon catalysts provide very high selectivities to higher hydrocarbons (C10-C20) and the CNT-supported catalyst is among the most active systems of all [138]. In parts this is related to the inertness of carbon preventing the formation of hardly reducible mixed metal oxides with the support, such as CoAl204 [139,140], which is, besides coking, the main reason for catalyst deactivation. The carbon surface functionalized with oxygen... 

The recent study by Lakshmi et al. [63] is just one example of the very extensive research efforts devoted to the improvement of performance of fuel cells by increasing the dispersion of the electrocatalyst on the carbon support by virtue of carbon surface functionalization [64], Without acknowledging their familiarity with the most relevant prior studies, they did note that the point of neutral charge evaluation helps in identifying the platinum complex to be used for electrocatalyst synthesis based on their charge, in the sense that, for example, if the carbon surface is positively charged an anionic platinum complex is needed (see Section 5.2.1). 

The catalytic role of carbon surfaces has been discussed in excellent reviews by Leon y Leon and Radovic [53] and by Radovic and Rodriguez-Reinoso [43] and is discussed extensively throughout this book. In this section, examples of the specific catalytic effect of carbon surface functionality are introduced only briefly. 

Physicochemical properties of carbon materials are investigated by means of various spectroscopic techniques, such as infrared (IR), X-ray photoelectron pCPS), electro spin resonance (ESR), or Raman spectroscopy (RS). These techniques provide very useful qualitative information about the carbon surfaces. A detailed discussion of the procedures and instruments used in these techniques is outside the scope of this chapter a brief overview is presented, to highlight the importance of the use of spectroscopic techniques to illustrate the carbon surface functionalities and to compare the results that arise from a consortium of methods. 

Figure 3(a) is the adsorption effect of modified Activated Carbon on Sb " with increasing pH. The pH was adjusted with HCl, selected room temperature, stirring frequency was lOOr/min, the amount of carbon was 5 g/L and the adsorption time was 1 h. The figure shows that with pH increased, activated carbon adsorption effect on Sb increased first and then decreased. When the pH was 5, the adsorption effect is better, and the remaining Sb " concentration dropped to 0.02 mg/L, removal rate was 99.13%. This is mainly because with the pH value increased, carbon surface functional groups will occur with the dissociation of H, thus exposed a large number of active centers, Sb + occupied the active center and effectively adsorbed, so the adsorption amount increased as the pH increased. However, as the pH increased, the chemical interactions between hydroxyl and the metal ions increased, resulted the relative decline in the amount of adsorption and thus activated carbon adsorption effect on Sb + increased first and then decreased. 

Phenol is the most extensively studied adsorbate for the adsorption of aqueous solutions on carbon, for practical (in waste water treatment) as well as scientific reasons. It is also a good model compound for organic pollutants in wastewater. Numerous factors are known to have significant effects on the adsorption of phenol pH of solution, type of carbon, carbon surface functionalities, oxygen availability ( oxic vs. anoxic condition), mineral contents of carbon, and addition of electrolytes. Typical isotherms, as a function of solution pH, are shown in Figure 5.12. The amount adsorbed is decreased at both high and low pH values. 

A carbon development program was initiated at the Illinois State Geological Survey (ISGS) and the University of Illinois at Urbana-Champaign (UIUC) to investigate the effects of different carbon types, carbon structures, and carbon surface functional groups on the rate and extent of adsorption of vapor-phase mercury. The results from a study to prepare Illinois coal-based activated carbons are presented. Carbon products were made both in bench- and pilot-scale reactors. 

Terzyk, A. P. 2003. Further insights into the role of carbon surface functionalities in the mechanism of phenol adsorption. Journal of Colloid and Interface Science 268(2) 301-329. 

An important probe of carbon surface functionality is mass spectrometry, in monitoring the nature of the gaseous phase produced from heated carbon fibers by temperature-programmed desorption (TPD). In the author s group TPD has been applied by heating the Fibers electrically while monitoring the temperature by optical pyrometry and the gaseous phase by mass spectrometry XPS data were recorded at the same time [8],... 

The comparisons made in Fig. 10 help to illustrate how the peak separations in the C l.v spectrum can be related to carbon surface functionality. The separations can be predicted by calculation as mentioned earlier, but model compounds can also give helpful information. In Figs. lOb and c are shown the spectra of solid hydroquinone at 77 K (an aromatic molecule with -C-OH functionality) and of solid benzoquinone (an aromatic molecule with -C=0 functionality), respectively. It is clear that the separation between the C l.v peaks arising from the aromatic ring (at lower binding energy) and from the -C-OH functionality is less than that between the former and that due to... 

In this section, we will consider the properties of perhaps the second most well developed of the electrochemical capacitor systems those based on the oxides of the transition and noble metals. In general, a distinction is made between the metal oxide systems and the carbon systems on the basis that the former are redox active materials, i.e., charge is stored by means of changes in the oxidation state of the metal when an ionic species (e.g., a proton) reacts with the surface (or bulk) of the oxide, and the chemisorption is accompanied by the simultaneous injection of an electron into the oxide. The carbon capacitors are supposed to be more purely of the double-layer or space-charge variety. In fact, as was pointed out earlier, the distinction is less clear. In the case of carbon, surface functional groups may be oxidized and reduced in very much the... 

---