High-surface-area active carbon formed

The two-stage process was licensed by Mitsui Mining Company (MMC) in Japan in 1982, and by 1993 a modified form of the process was installed in four commercial plants in Japan and Germany [58]. The granular carbon or activated coke used in this process has a surface area of initially 150 to 250 mVg, which is much lower than that of commercial activated carbons. It is produced from a bituminous coal and a pitch binder. Low surface area carbons have been found to be the most effective in this process they are cheaper than high surface area activated carbons, they retain their SO2 adsorption capacity more efficiently on repeated cycling, and their relatively low porosity contributes to strength and abrasion resistance. 

High surface area activated carbon fibers were first prepared by direct carbonization and activation of phenolic fibers in steam/CO2 environment at temperatures around 1000°C (Economy and Lin 1976). These activated carbon flbers, manufactured in the form of a fabric, have received increased attention as adsorbents in air treatment processes. Because these fabrics are easy to handle, there is an increasing demand for them in various applications such as protective fabrics, filtration devices, odor absorbents, and for a wide range of ancillary industrial applications. The high cost of these fabrics has limited their potential use for a number of applications. High cost is also an issue for their use in military applications (Mangun et al. 1999). 

Care had to be taken to load the ion exchange resin into the adsorption cell of the FMC in such a way as to allow for its swelling when wetted by water. For resin used in the author s work, Amberlite IR120, the swelling amounted to one third of the original volume of the resin. The adsorption of water by the dry resin in its acid form caused a sharp heat of wetting which was similar to those produced by high surface area activated carbons and zeolites. 

New high-surface-area zirconia-carbon composites were prepared by a sol-gel method followed by a high-temperature treatment in inert gas.420 The samples proved to be very active and selective in the aromatization of Cg+ alkanes (n-hexane and n-octane). From n-octane, as main products, only ethylbenzene and o-xylene were formed. The catalysts have low acidity due to significant dehydration of the zirconia surface, and high surface area since the carbon matrix prevents sintering of the Zr02 particles. 

Reaction between metal oxide vapor and solid carbon. A novel method of preparation of ultra-high surface area carbides55-59 involves the reaction of solid carbon with vaporized metal oxide precursors like Mo03 or WO2. The synthesis uses high specific surface area activated carbons and the final product appears to retain a memory of the porous structure of the starting material. The carbon acts like a skeleton around which the carbides are formed, and catalytically active samples with surface areas between 100 and 400 m2g 1 are generated. Materials prepared by this method are described by Ledoux et al. (chapter 20). 

Porous carbons constitnte a fascinating kind of material. Different types with distinctive physical forms and properties (i.e., activated carbons, high-surface-area graphites, carbon blacks, activated carbon cloths and fibers, nanofibers, nanotubes, etc.) find a wide range of indnstrial applications in adsorption and catalysis processes. The main properties of these materials that make them very useful as catalyst supports, as well as some of their applications, have been described. The use of carbon as a catalyst support relies primarily on the relative inertness of its surface, which facilitates the interaction between active phases or between active phases and promoters, thus enhancing the catalytic behavior. This makes porous carbons an excellent choice as catalyst support in a great number of reactions. 

High Surface Sodium. Liquid sodium readily wets many soHd surfaces. This property may be used to provide a highly reactive form of sodium without contamination by hydrocarbons. Powdered soHds having a high surface area per unit volume, eg, completely dehydrated activated alumina powder, provide a suitable base for high surface sodium. Other powders, eg, sodium chloride, hydride, monoxide, or carbonate, can also be used. 

As described above, XAS measurements can provide a wealth of information regarding the local structure and electronic state of the dispersed metal particles that form the active sites in low temperature fuel cell catalysts. The catalysts most widely studied using XAS have been Pt nanoparticles supported on high surface area carbon powders,2 -27,29,so,32,33,38-52 represented as Pt/C. The XAS literature related to Pt/C has been reviewed previ-ously. In this section of the review presented here, the Pt/C system will be used to illustrate the use of XAS in characterizing fuel cell catalysts. 

The complex three-dimensional structure of these materials is determined by their carbon-based polymers (such as cellulose and lignin), and it is this backbone that gives the final carbon structure after thermal degradation. These materials, therefore, produce a very porous high-surface-area carbon solid. In addition, the carbon has to be activated so that it will interact with and physisorb (i.e., adsorb physically, without forming a chemical bond) a wide range of compounds. This activation process involves controlled oxidation of the surface to produce polar sites. 

The enormous importance of carbon in such diverse fields as inorganic and organic chemistry and biology is well known however, only the aspects of carbon relevant to catalysis will be described here. The main topics we are concerned with are porous activated carbons, carbon black as catalyst supports and forms of coking. Carbon is also currently used as storage for natural gas and to clean up radioactive contamination. Carbon is available at low cost and a vast literature exists on its uses. Coal-derived carbon is made from biomass, wood or fossil plants and its microstructure differs from carbon made from industrial coke. Activated carbons are synthesized by thermal activation or by chemical activation to provide desirable properties like high surface area. 

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