Surface Oxygen Groups

FIGURE 2.32 Significant oxygen surface groups on a carbon surface (a) carboxyl, (b) lactone, (c) carbonyl, (d) ether, (e) pyrone, (f) phenol, and (g) carboxyl anhydride. 

Gou ec, R, Savy, M., and Riga, J., Oxygen reduction in acidic media catalyzed by pyrolyzed cobalt macrocycles dispersed on an active carbon the importance of the content of oxygen surface groups on the evolution of the chelate structure during the heat treatment, Electrochim. Acta, 43, 743, 1998. 

The third method (OCI) avoids these errors, since the physisorbed oxygen is quantified and eliminated from the final ASA calculation. Moreover, the evaluation of the chemisorbed oxygen does not require the oxygen surface groups formed to evolve, since the chemisorbed oxygen is evaluated from the direct measurement of the variations in oxygen pressures during the chemisorption process. 

Effective density. The diameter and volume of the micropores were determined by the measurement of the density using as displacement molecules with different sizes of effective diameter, e g., helium (0.25 nm), water (0.264 nm), benzene (0.370 x 0.528 nm), and decaline (0.472 X 1.01 X 0.624 nm). All pycnometric fluids are non-polar, except water. This adsorbate was used for the sake of the little diameter of its molecule. In the case of CMSs studied - not including of oxygen surface groups [8] - water molecule is good molecular probe. 

Rodriguez-Reinoso, F., Molina Sabio, M., and Gonzalez, M.T. (1997). Effect of oxygen surface groups on the immersion enthalpy of activated carbons in liquids of different polarity. Langmuir, 13, 2354-8. 

Figure 2.5 Proposed model for stabilization of carbon surfaces upon heat treatment () in N2 (inert gas) and H2. For simplicity and illustrative purposes, only two types of oxygen surface groups (pyrone and lactone) and three other types of active sites are shown. These three types are in order of increasing stability (1) type I isolated unpaired-electron sites Ar-X (where Ar represents the aromatic (graphene layer) (2) type II, Ar-C=CX and (3) type II, divalent in-plane a pair, Ar-Xs (where s represents a localized n electron). Structures C and D are formed in H2. Structure D is much more abundant in H2-treated carbons because of the higher concentration of CH2 radicals. (From ref. 84, with permission. Copyright 1996 American Chemical Society.)...

Analysis of the enthalpy of immersion in water can also lead to information about the number of primary adsorption centers of activated carbons and oxygenated surface groups. The relationship between these two quantities was proposed by Stoeckli and co-workers [281] ... 

Precipitation or coprecipitation methods are also often used. Suh et al. [40] analyzed the effect of the oxygen surface functionalities of carbon supports on the properties of Pd/C catalysts prepared by the alkali-assisted precipitation of palladium chloride on carbon supports, followed by liquid-phase reduction of the hydrolyzed salt with a saturated solution of formaldehyde. They observed that the metal dispersion increased with increasing amount of oxygen surface groups. Nitta et al. [41] also used a deposition-precipitation method, with sodium carbonate and cobalt chloride or nitrate, to prepare carbon-supported Co catalysts for the selective hydrogenation of acrolein. 

---