Adsorption on carbon materials

R. Strobel, L. Jorissen, T. Schhermann, V. Trapp, W. Schutz, K. Bohnhammel, G. Wolf, J. Garche, Hydrogen adsorption on carbon materials. J. Power Sources, 84(2) (1999) 221-224. 

Competitive adsorption on carbon was also studied. The results are shown in Figure 34.8. The product PG competitively adsorbs to carbon more readily than the starting material. This can have implications in reaching full conversion and on product stability. The impact of the relative adsorption is alleviated under continuous flow reactor conditions where we are able to achieve high conversion and high yield. A full accounting of the adsorption work will be the subject of a later publication. 

E. Horozova, N. Dimcheva, and Z. Jordanova, Adsorption, catalytic and electrochemical activity of catalase immobilized on carbon materials. Z Naturforsch. 52, 639-644 (1997). 

The experimental results obtained with carbon nanofibers and nanotubes fit into the tendencies obtained with the other type of carbon materials, indicating that hydrogen adsorption on these materials is also taking place by a physisorption process. 

Figure 6. Isotherms of hydrogen adsorption and desorption on carbon materials at temperature 77K, measured by the High Speed Gas Sorption Analyser NOVA 1200.

Two different technologies seem to be the most promising alternatives to reduce gaseous PAH emissions catalytic PAH destruction [6, 7] and PAH adsorption on carbonaceous materials [8, 9]. Historically, carbonaceous materials have been used for the removal of vapor phase organic compounds from about 100 ppmv to 10,000 ppmv concentrations in industrial waste gas streams [10]. Recently, it has been shown that dioxins, furans and PAH, at ppbv or lower coneentrations, can be effectively removed from waste incinerator combustion gases by using carbon injection or carbon bed technology [11]. 

Method 1 includes three main stages. These are addition of the H2PdCl4 solution to the aqueous suspension of the support, hydrolysis of Pd compounds with an introduced alkali agent, followed by reduction. As pointed out at the beginning of Section 12.2.4, when Pd/C is synthesized by any of these methods, addition of the Pd solution to carbon slurry results in adsorption of a portion of Pd compounds on the support. Figure 7 (a) shows mononuclear Pd complexes to be better adsorbed from the acidic medium (method 1) than from the alkali one (method 2). Therefore, the above-mentioned primary processes will mostly affect the catalysts prepared by method 1. Hence, analysis of the literature data concerned with this method of the Pd/C catalysts preparation should be based on the data on studying the adsorption of H2PdCl4 on carbon materials. 

Zhou, A.N., Ma, X.L., and Song, C.S. Liquid-phase adsorption of multi-ring thiophenic sulfur compounds on carbon materials with different surface properties. The Journal of Physical Chemistry. B, 2006, 110, 4699. 

Commercial activated carbon was found to be more efficient as adsorbent of quinoline than common inorganic materials [11]. Adsorption of quinoline on activated carbon increases with pH up to pH 6 and at pH 6-11 the adsorption is nearly constant. In contrast the adsorption on inorganic materials has a sharp maximum at pH about 6. 

This chapter is concerned with the energetics of gas adsorption on carbons, or more specifically the thermodynamic quantities involved when carbon materials are employed as the adsorbents. Out of these solids, activated carbons, due to their exceptional surface area development and consequent technological implications, are the carbonaceous adsorbents that have attracted the attention of most publications. A more comprehensive account of the energetic aspects of adsorption on carbons has been published elsewhere [1]. 

Groszek, A.J. (1998). Flow adsorption microcalorimetry. Thermochim. Acta, 313,133—43. 70. Moreno-Castilla, C. (2004). Adsorption of organic molecules from aqueous solutions on carbon materials. Carbon, 42, 83—94. 

As the experimental and theoretical investigations of gas adsorption on carbon nanotubes progressed, a number of questions that are important from a fundamental perspective have emerged. These questions provide an independent scientific motivation for the study of adsorption of various gases on these novel carbon materials. 

Perez-Mendoza, M., Domingo-Garcia, M., and Lopez-Garzon, FJ. (2000). Adsorption of methylamines on carbon materials at zero surface coverage. Langmuir, 16, 7012-18. 

Since the initial proposals by Coughlin and Mattson, many published papers have attempted to elucidate the most appropriate mechanism to explain the adsorption of phenolic compounds and of aromatic compounds in general on carbon materials. Perhaps the first experimental evidence of the Tr-ir dispersion interaction mechanism was provided by Mahajan and coworkers [19] in their study of phenol adsorption on graphite and boron-doped graphite samples. They reported that the presence of substitutional boron in the lattice of polycrystalhne graphite, which removes ir-electrons from the solid, results in a lowering of the phenol uptake from water. 

Surfactants will be the last type of organic electrolyte to he studied in this section. These molecules are amphiphilic, due to their dual hydropho-bic/hydrophilic character. This produces their accumulation at soHd-water interfaces, where both the hydrophobic and the hydrophihc parts participate in favorable intermolecular interactions. Surfactants are widely used in many industrial and commercial products and processes and have an environmental impact on wastewaters. In recent years, several studies have been pubUshed on the adsorption of surfactants on carbon materials [11, 45-48], and the main results obtained in these works are presented below. 

The essential aim of this work is to fill the gap that exists between the fields of adsorption and carbon materials, an area that, to our knowledge, has not been encompassed so far in one single book. Several books address the phenomenon of adsorption from both a fundamental and an applied perspective, while publications on the structure, properties, and applications of carbons, either general or restricted to specific types of materials, are increasingly common. There are, also, a number of works devoted to porosity in carbons or other solids. However, adsorption is involved in many areas other than porosity characterization. In short, the interplay between adsorption and carbon materials has not been addressed yet in one volume. There is a vacuum of knowledge between both fields that, if filled, could give birth to new concepts and ideas. 

Recently, carbon molecular sieves have been fabricated in the form of planar membranes and hollow tubes by the pyrolysis of polyacrylonitrile in suitable forms (12-16). Very high separation selectivities have been reported with these materials. Their pore sizes are in the range from 3 to 5.2A. Selectivities of greater than 100 1 are observed between molecules which differ by as little as 0.2A in their critical dimensions. Kinetics of adsorption on these materials have been determined (2.,ii,l ) -... 

In this chapter we shall contemplate theories that have been offered to interpret varied aspects of adsorption on carbon.1,2 For this, it is well to comment briefly on the role of a theory as we envision it. Theories are to be viewed, not as blue-prints to portray the inner working of a phenomenon, but rather as mental inventions that enable us to make more effective use of the material world. 

Hydrogen physisorption on pure carbon materials will not meet DOE targets, owing to the thermodynamic enthalpy of hydrogen adsorption on carbon. For instance, our previous work on SWNTs yielded a value of 38 milli-electron volt [1] or 3.6 kilojoule per mole (kJ/mole), values consistent with adsorption on a graphene surface [2]. Our work for... 

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