Surface groups carbonyl

There is ample evidence in the literature for conversion of reactive hydrocarbons to carbonyl compounds by autoxidation. In coals, the final products of autoxidation under the conditions used in the present study could be a mixture of carbonyl and carboxylic acid surface groups. Under mild oxidation conditions, a different set of functional groups such as ethers as proposed by Liotta et al. or epoxides as suggested in Scheme V could be formed. There are numerous examples of alkoxy radicals rearranging to epoxides . Choi and Stock have shown that ethers can be produced from benzhydrol structures, which are invoked as intermediates in Scheme IV. At higher temperatures, the epoxides and ethers are unstable and may rearrange to carbonyl compounds. 

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. 

Oxygen is the main heteroatom in the carbon matrix, and the occurrence of functional groups, such as carboxyl, carbonyl, phenols, ends, lactones, and quinones, has been suggested [176,181], These surface groups can be produced during the activation procedure and can as well be introduced subsequent to preparation by an oxidation treatment [178] (see Figure 2.32). 

The diverse types of oxygen functional groups determine the acidic and basic character of the carbon surfaces [175,182], The acidic character is typically linked with surface complexes like carboxyl, lactone, and phenol, while the basic nature is regularly assigned to surface groups, such as pyrone, ether, and carbonyl [173,178] (see Figure 2.32). 

Boehm s procedure [6] was used to titrate carboxyls, lactones, phenols and carbonyls functional surface groups. 

Adsorption enthalpies are also very similar but quite different pre-exponential factors are obtained. This indicates that the same sites are involved for the adsorption of NO but their number has increased. The increase of the number of active sites can be confirmed by TPD experiments obtaining that the total amount of CO and CO2 increased considerably after treatment of the raw sample (Table 2). On the other hand, the amount of different type of surface groups varies in a low extent after treatment of the raw sample, except for the carbonyls that increases in concentration by approximately a factor of three. So, these structures could be the responsible of the enhancement of the NO conversion once determined that diffusion coefficients are similar for both samples. 

To obtain H NMR spectra for water molecules interacting with surface oxidized groups (carbonyls, carboxyls, hydroxyls), NMR investigations have been made on frozen aqueous suspensions of graphite oxide (GO) [93,94], Graphite oxide is constituted by colloidal particles consisting of completely oxidized... 

Let us call this the donor-acceptor complex proposal, similar to that presented recently for adsorption of substituted nitrobenzenes and nitrophenols on mineral surfaces [739]. The experiments on which this proposal is based are (1) isotherms of phenol, nitrobenzene, and m- and / -nitrophenol on one commercial activated carbon at pH = 2-7 and very low solute concentrations ( <1.5% of the solubility limit of these species [6]) and (2) detailed infrared (internal reflection) spectroscopic analysis of the surface after adsorption of / -nitrophenol. Interestingly, neither in this study, nor in any subsequent study that supports this mechanism, has a similar analysis been performed with carbons containing varying concentrations of carbonyl surface groups. Also of interest is that the authors dismiss the electrostatic explanation of the reported pH effects by assuming that the isoelectric point of the carbon (which was dried at 200°C for 12-24 h) was ca. 2.4. 

As in the case of catalysts for oxygen reduction, the surface properties of Pt catalysts for methanol oxidation are governed by both the preparation method and the nature of carbon support. As discussed above, the presence of surface groups such as carboxylic, carbonyl, phenolic, lactone, and pyrone functionalities determine... 

In terms of availability, number, and nature of surface groups, surface area, pore size, pore volume, and form and size of the particles, silica has been undoubtedly the most preferred inorganic support. Suitable modification is possible via the surface silanol groups, which can react either directly with an appropriate metal complex or with an intermediate ligand group. Direct surface bonding has often been practiced, e. g., for the anchoring of metal carbonyl complexes [14] (eq. (11)), carbonyl clusters [26], polymerization catalysts [21, 62], or other special systems, e. g., 7r-allyl complexes [63] or metalloporphyrins [64]. 

Still, when using porous carbons, the desorption of newly generated styrene from the catalyst surface was found to be hindered, and so the conversion was Hmited. The lack of any porosity in carbon onions should clearly be beneficial here, and indeed the conversion and the yields of styrene could be increased when using nano-onions or onion-Uke materiaL In samples of catalyst that had already been used, the onion stracture was found to be partly destroyed. Actually, the catalyst reaches full activity only in this state, which also accounts for the induction period observed. On the onions surface, presumably carbonyl groups and quinoid structures constituting the real active sites are formed. 

Further purification is achieved by a treatment with concentrated mineral acids at high temperature and, in parts, elevated pressure. One procedure commonly applied uses concentrated nitric acid, which removes the metalUc impurities as well as the portion of sp -hybridized carbon. The particulate metals or metal oxides are dissolved, while the amorphous carbon is oxidized to be CO2 in the end. The diamond, on the other hand, is conserved due to its lower reactivity toward mineral acids. Further reagents to be employed besides nitric add include sulfuric or perchloric acid as well as mixtures of hydrochloric with sulfuric acid or hydrogen peroxide with sulfuric add. The intention is always to dissolve the impurities and to selectively oxidize the graphitic carbon. Especially with perchloric acid, a significant functionalization of the partide surface with carbonyl and carboxyl groups occurs, whereas with sulfuric or nitric acid, it does not happen to that extent... 

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