Mesoporous carbons

Palladium is known to be a metal that works catalytically in the system. Various supports can be used for Pd, such as active carbon, mesoporous materials, and polymers. All of them deactivate in the sitosterol hydrogenation, most probably because of sulfur and phosphorus impurities present in the raw material, which originates from the tall oil production, a side process of chemical pulping. 

Porous carbons were prepared using MCM-48 and SBA-15 mesoporous templates and various carbon precursors (see Chapter 3 for preparation description). Figure 8.11 displays the nitrogen adsorption isotherms at 77 K of SBA-15 and of the corresponding templated carbon obtained by carbonization of sucrose in the template. Both isotherms show a bimodal porosity in the templated carbon, mesopores are generated by the removal of the silica walls, and micropores are present in... 

CMK-1 carbon was the first carbon material reported to exhibit well-resolved XRD lines characteristic of ordered arrays of carbon mesopores [3]. The synthesis of the carbon was achieved by carbonization of sucrose inside the MCM-48 mesoporous silica. As shown in Fig. 2, the XRD pattern exhibits a new diffraction line around 1.4 compared with its MCM-48 template. This change can be explained by the formation of two separate carbon networks in the bicontinuously mesoporous MCM-48 template. After the separating silica frameworks are removed, the two carbon networks join together. The joining of the two carbon networks attributes to the syirunetry change from cubic Io3d to either 74,/a or lower [12]. The new ordered mesoporous structure is indicated by the XRD pattern and transmission electron microscopic image shown in Fig. 2. 

Hanazawa, Y. and Kaneko, K. (1997). Lack of a predominant adsorption of water vapor on carbon mesopores. Langmuir, 13, 5802-4. 

Lately, a fascinating strategy has been successfully developed for the preparation of ordered mesoporous carbons. The synthesis procedure of these advanced carbons consists in the infiltration of an organic precursor into the pores of silica or aluminosilicate templates, followed by the subsequent pyrolysis of the precursor and dissolution of the template framework by HF [9—12]. In another process, carbon is directly introduced in the template by a CVD method [86]. The method gives a highly ordered and interconnected network of meso- and micropores [87], where the size of carbon mesopores is defined by the walls thickness of the pristine silica matrix. Such materials are very suitable for better understanding the relationships between the porous characteristics and the supercapacitors performance [88, 89]. 

Other Ordered Mesoporous Silicas as Hard Template Other mesoporous silicas including MCM-41, HMS, MSU-1, MSU-H, SBA-1, SBA-7, SBA-12 and SBA-16 have also been explored as hard templates to fabricate mesoporous carbons. Mesoporous silica MCM-41, which has hexagonally ordered cylindrical one-dimensional pores, was found to be unsuitable as a template for mesoporous carbon as its use yielded disordered high surface area microporous carbon. This is due to the absence of complementary micropores within the MCM-41 silica walls. However, Tian et al. have successfully produced self-supported, ordered, ultrathin carbon nanowire arrays by employing the mesoporous silica MCM-41 as template.The carbon nanowire arrays exhibit high surface areas up to 1400 m g , large pore volumes of 1.1 cm g and uniform mesopore size of ca 2.2 nm. 

Carbon-based soUd acids with high surface areas have been also reported. SOjH-modified amorphous carbon/mesoporous sihca SBA-15 composites showed a distinct activity for a hydrophobic acid-catalyzed reaction, the dimerization of a-methylstyrene, whereas bulk carbon-based acids were completely inactive [72]. 

Leboda, R., Marciniak, M., Gun ko, V.M., Grzegorczyk, W., Malygin, A.A., and Maikov, A.A. 2000a. Structure of carbonized mesoporous silica gel/CVD-titania. Colloids Surf. A Physicochem. Eng. Aspects 167 275-285. 

Volume-Imprinted Surface-Imprinted Mesoporous Carbon Mesoporous Carbon... 

Kaukonen AM, Laitinen L, Salonen J, Tuura J, Heikkila T, LimneU T, Hirvonen J, Lehto VP (2007) Enhanced in vitro permeation of furosemide loaded into thermally carbonized mesoporous silicon (TCPSi) microparticles. Eur J Pharm Biopharm 66 348-356 Kawamura YL, Sakka T, Ogata YH (2005) Photoassisted control of Pt electrodeposition on p-type Si. J Electrochem Soc 152 C701-C705... 

Liu, S.-H., Yu, W.-Y, Chen, C.-H., Lo, A.-Y, Hwang, B.-X, Chien, S.-H. Liu, S.-B. Fabrication and characterization of well-dispersed and highly stable PtRu nanoparticles on carbon mesoporous material for applications in direct methanol fuel-cell. Chem. Mater 20 (2008), pp. 1622-1628. 

For all processes that involve the adsorption step, such as physical processes of separation or catalytic transformations, the usage of solid materials with optimised activity as adsorbents and catalysts is necessary. Various solids, such as porous materials (zeolites—molecular sieves with hierarchical porosities and natural clays), activated carbons, mesoporous silica-based materials, pillared clays and metal oxides, have shown the ability to act as adsorbents or as catalysts for the conversions of previously mentioned atmospheric pollutants. Solid materials are also used for the removal of pollutants that can be found in wastewaters. The possibilities to remove polyaromatic hydrocarbons (PAHs) and heavy metal particles using the adsorptive characteristics of activated carbon and porous materials from wastewaters have been proven [15-17]. The same classes of solids are used for the elimination of organic pollutants form wastewaters by heterogeneous catalytic oxidation processes one of the most important tasks is to eliminate phenolic compounds [13]. 

FIGURE 20. Syntheses of mesoporous carbon, mesoporous carbon nitride, mesoporous boron nitride, and mesoporous boron carbon nitride. 

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