Surface acidic functional

The surface area, the pore size, and the carbon yield are greatly influenced by oxidizing gas, heat-treatment temperature, and activation time. In addition, the oxidative activation introduced the surface acidic functional groups (SAFGs) on the pore surfaces of the carbon. The amounts of the SAFGs can be also controlled by... 

It was found by Nis XPS studies of pyridine-adsorbed samples that after deactivation the surface acidic function changes in a different manner with the bulk acidity measured by infrared characteristic absorption bands of pyridine adsorbed samples [7], which would suggest different distributions of the acidic properties in the sample catalysts. The effects of additive elements on the overall acidic features of modified zeolite catalysts are dependent on sample pretreatment and/or reaction condition, which will contribute differently to the induced acidity on the surface and in bulk bifunctional properties, as examined by the reaction of n-heptane shown in Figure 1. 

Soft oxidation does not change the surface area, even if it is performed for a very long time. After ten days, surface area is still higher than 710 mig. On the contrary, severe oxidation directly influences the surface area of the support, leading to a complete destruction of the structure of the active carbon 95 % of the surface area can be lost. The solid becomes very difficult to recover by filtration. In Fig. 2, we can see that the destruction of the support is non-linear vs. time. The beginning of the dislocation of the aromatic sheets occurs between 45 and 65 minutes, corresponding to a slowdown of the creation of surface acidic functions (also represented in Fig. 2). 

Yoshida and co-workers [161] studied the relationship between the EDL properties in an organic electrolyte solution and the concentration of surface acidic groups of phenolic resins-based activated carbon fibres. The authors reported that EDL capacitors with high capacitance and low leakage current were obtained with ACF that showed an extremely low concentration of surface acidic functional groups per unit surface ar ... 

Standard deviation of the distribution variables Surface acidic functional group Saturated calomel electrode Scanning electron microscopy Single-probe... 

In the 1960s, carbon blacks were mainly prepared by channel processes, and their acidic functions were present at about 10 eq/g, which allows relatively easy determinations but now, with furnace blacks, the surface acidic functions are generally of about 10 eq/g, and specific techniques (Bertrand and Weng, 1998) or drastic reaction conditions must be used (Custodero et al., 1992). Obviously, such delicate determination must be conducted on previously extracted black, in order to eliminate basic mineral impurities that would hinder any characterization of the rare acidic groups present on carbon black. 

Yoshida, A., I. Tanahashi, and A. Nishino. 1990. Effect of concentration of surface acidic functional groups on electric double-layer properties of activated carbon fibers. Carbon 28 611-615. 

Crocidolite In vitro Surface iron after reduction to Fe" and chelation by citrate Corresponding to decrements in surface F, thiobarbiturate-reactive products and HO. diminished. Deferoxamine provides similar results by chelating Fe. Ghio etal. 1992 Surface acidic functional groups... 

Methanol dehydrogenates to methyl formate over fresh WC and P-W2C powders with selectivities higher than 90% (109,110). The dominant side reaction is the decomposition to synthesis gas. Over WC and P-W2C modified with oxygen, methanol selectively dehydrates to dimethylether at 473 K and at higher reaction temperatures, C2-C4 olefins are produced (47). Thus, the dehydrodimerization of methanol apparently requires WC sites. These sites are titrated by chemisorbed oxygen. Thus, oxygen on the surface inhibits the formation of methyl formate and introduces a surface acid function WO that catalyzes dehydration by carbenium-ion type catalysis. 

Oxidation and chlorination of the catalyst are then performed to ensure complete carbon removal, restore the catalyst chloride to its proper level, and maintain full platinum dispersion on the catalyst surface. Typically, the catalyst is oxidized in sufficient oxygen at about 510°C for a period of six hours or more. Sufficient chloride is added, usually as an organic chloride, to restore the chloride content and acid function of the catalyst and to provide redispersion of any platinum agglomeration that may have occurred. The catalyst is then reduced to return the metal components to their active form. This reduction is accompHshed by using a flow of electrolytic hydrogen or recycle gas from another Platforming unit at 400 to 480°C for a period of one to two hours. 

Once a metal surface has been conditioned by one of the above methods, a coupling agent composed of a bifimctional acid—methacrylate similar to a dentin adhesive is appHed. This coupling material is usually suppHed as a solvent solution that is painted over the conditioned metal surface. The acidic functional group of the coupling molecule interacts with the metal oxide surface while the methacrylate functional group of the molecule copolymerizes with the resin cement or restorative material placed over it (266,267). 

Generally, the interaction of polar analytes with the packing is rather weak due to the hydrophilic polyhydroxy functions on the surface of the packing. However, small amounts of acidic functional groups are present on the surface of the packing. The influence of these functional groups can be suppressed easily with the use of salts in the mobile phase. 

Catalytic processes frequently require more than a single chemical function, and these bifunctional or polyfunctional materials innst be prepared in away to assure effective communication among the various constitnents. For example, naphtha reforming requires both an acidic function for isomerization and alkylation and a hydrogenation function for aromati-zation and saturation. The acidic function is often a promoted porous metal oxide (e.g., alumina) with a noble metal (e.g., platinum) deposited on its surface to provide the hydrogenation sites. To avoid separation problems, it is not unusual to attach homogeneous catalysts and even enzymes to solid surfaces for use in flow reactors. Although this technique works well in some environmental catalytic systems, such attachment sometimes modifies the catalytic specifici-... 

Figure 6. Simulated cyclic voltammogram for the oxidation of ascorbic acid without Inclusion of ec catalysis by the surface qulnone functionalities. Filled circles represent the simulated data and an experimental curve Is shown with a line for comparison. A scan rate of 100 mV s was assumed for experimental and simulated data.

Figure 2. Catalytic activities of CsxH3-xPWi2O40 for decomposition of isopropylacetate as a function of the surface acidity. The reaction was carried out at 373 K in liquid-solid reaction system.

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