Hierarchical carbon templating

In addition, experiments of isobutane diffusion reveal that the effective diffusivity is three times higher over a carbon-templated hierarchical zeolite [143]. Similar conclusions were drawn by Groen et al. [144] with hierarchical zeolites synthesized using the desilication method, where a two-order-magnitude improvement was observed in the diffusion of neopentane inside desiUcated ZSM-5 because of the shorter diffusion path length and presence of an accessible network of mesopores. 

Hard Templating by Carbon Materials The work on carbon templating by Jacobsen and coworkers [156] has stimulated dramatic growth in the synthesis of mesoporous/hierarchical zeolites. This approach uses an excess of zeolite gel inside an inert, mesoporous carbon matrix, wherein the zeohte grows over and... 

Carbon templating offers many possibilities for the synthesis of hierarchical zeolites because of the large availabihty of carbon materials that can be employed. 

Hard-Templated Microporous, Mesoporous, and Hierarchical Carbons.332... 

Zeolite materials with tunable size and volume of mesopores can be prepared by using dispersed carbon black particles with narrow distribution of their sizes as inert mesoporous matrix or as secondary template. In such confined space for synthesis the crystallization of zeolite gel occurs inside the interparticle voids of carbon matrix [10,11,12]. In the case of generation of mesopores by secondary templating by means of addition of carbon black into the reaction mixture, zeolite crystals are formed around carbon particles [13]. After burning off a carbon matrix or carbon particles, zeolite crystals with a controlled pore size distribution and a crystalline micro-mesoporous hierarchical structure are prepared. 

Sen T, Tiddy GJT, Casci JL, Anderson MW (2004) Synthesis and characterization of hierarchically ordered porous silica materials. Chem Mater 16 2044 Deng Y, Liu C, Yu T, Liu F, Zhang F, Wan Y, Zhang L, Wang C, Tu B, Webley PA, Wang H, Zhao D (2007) Facile synthesis of hierarchically porous carbons from dual colloidal crystal/block copolymer template approach. Chem Mater 19 3271 Luo Q, Li L, Yang B, Zhao D (2000) Three-dimensional ordered macroporous structures with mesoporous silica walls. Chem Lett 29 378... 

Monolithic carbons are easier to handle than powdered materials. Direct shaping of monolithic mesoporous carbons during their preparation is highly desirable. Mesoporous carbon monoliths may be fabricated by using mesoporous silica monoliths as template. Carbon monoliths with well-developed and accessible porosity have been produced using silica monoliths with a hierarchical structure containing macropores and meso-pores as templates and furfuryl alcohol or sucrose as a carbon precur-... 

Ordered mesoporous carbons, prepared by nanocasting, have also been used successfully as templates for the synthesis of hierarchical zeolites [159, 160). This is the case of CMK-3, an ordered mesoporous carbon attained by nanoreplication of pure silica SBA-15. The hierarchical zeolites obtained by employing CMK-3 as a template mainly present supermicropores or small mesopores with a size around 2 nm. The textural properties of the hierarchical zeohtes can be tuned by changing the type of CMK-3 carbon used. A modification of this method consists of directly impregnating the composite SBA-15-carbon or MCM-41-carbon with TPAOH and leaving the mixture crystallizing hydrothermally under steam. After calcination, a mesoporous ZSM-5 is formed with mesopore sizes around 3.5 and... 

S.3.2.2.4 Hard Templating by Polymers Another option for the synthesis of hierarchical zeohtes is the apphcation of polymers as hard templates, a strategy closely related to the use of carbons as hard templates. Several polymers have been used for this purpose. For example, polystyrene beads have been employed for obtaining hierarchical zeolites with a microporous/macroporous structure [161]. 

Mun, Y, C. Jo, T. Hyeon et al. 2013. Simple synthesis of hierarchically structmed partially graphitized carbon by emulsion/block-copolymer co-template method for high power supercapacitors. Carbon 64 391-402. 

Fulvio PF, Hillesheim PC, Oyola Y, Mahurin SM, Veith GM, Dai S (2013) A new family of fluidic precursors for the self-templated synthesis of hierarchical nanoporous carbons. Chem Commun 49 7289-7291... 

Carriazo D, Gutierrez MC, Ferrer ML, del Monte F (2010) Resorcinol-based deep eutectic solvents as both carbonaceous precursors and templating agents in the synthesis of hierarchical porous carbon monolith. Schem Mater 22 6146-6152... 

Zeng Q, Wu D, Zou C, Xu F, Fu R, Li Z, Liang Y, Su D (2010) Template-free fabrication of hierarchical porous carbon based on intra-Zinter-sphere crosslinking of monodisperse sty-rene-divinylbenzene copolymer nanospheres. Chem Commun 46 5927-5929... 

Adelhehn P, Hu Y-S, Chuenchom L, Antonietti M, Smarsly BM, Maier J (2007) Generation of hierarchical meso- and macroporous carbon from mesophase pitch by spinodal decomposition using polymer templates. Adv Mater 19 4012-4017... 

Very recently, Broda and Muller [87] extended the carbon sol-gel technique first reported by Pekala [88] to synthesize Al203-stabilized, CaO-based CO2 sorbents with a hierarchical pore structure. It was argued that by nanostructuring the material, diffusive limitations of the carbonation reaction could be avoided. Here, a carbon gel acted as a template for pores in the small micrometre range. A schematic sketch of the different steps of the synthesis protocol is shown in Fig. 6.31. In the first step, formaldehyde was added to an aqueous solution of resorcinol to obtain a molar ratio of resorcinol to formaldehyde of 1 2. Subsequently, an... 

Continuous mesoporous carbon thin films were fabricated by direct carbonization of sucrose-silica nanocomposite films and subsequent removal of the silica [236]. The mesoporous carbon film with uniform and interconnected pores had a surface area of 2603 mVg and a pore volume of 1.39 cmVg. Subsequently, nanoporous carbons with bimodal PSD centered at about 2 and 27 nm in diameter were prepared by using both the TEOS-derived silica network and the colloidal silica particles as templates [237]. Figure 2.33 illustrates the preparation pathway. The pore sizes of the carbon are determined by the sizes of the added silica particles and the silica network. As the colloidal silica particles are commercially available with different diameters (e.g., 20 to 500 nm), this dual template synthesis process provides an efficient route to preparing nanoporous carbons with a controllable hierarchical pore structure. 

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