Disordered mesoporous carbon

Recently, much study in the field of catalysis has sought interest in carbons with controllable pore diameters usually ranging from 2 to 50 nm. These mesoporous carbons can be classified into two categories, namely, ordered mesoporous carbons (OMCs) and disordered mesoporous carbons (DOMCs). OMCs can be synthesized by casting hard silica templates and impregnating a carbon source into the pores of the sihca or by directly templating a triblock copolymer. OMCs are usually preferred over DOMCs... 

A catalyst that can prevent polysulfide anions from precipitating as solids would be highly desirable. While a catalyst still remains to be discovered, several approaches, common in catalysis, have been employed to improve the cycling performance of lithium-sulfur batteries. For example, new electrolytes [18-21], protective films [22], solubiHzed sulfides [23], and new cathodes [24] have been developed. However, the performance results have either not been reported or have been found to be inadequate for practical applications. For example, a disordered mesoporous carbon-sulfur composite in conjunction with ionic liquid electrolytes has been fabricated. This system achieves high initial capacity that deteriorates rapidly [20]. 

Despite the advantages offered by CNTs and CNFs, there are still many obstacles (cost, synthesis methods) to overcome to allow large-scale production. Another type of catalyst support material is mesoporous carbon that provides high surface area and conductivity [100, 141]. It can be classified into ordered (OMC) and disordered (DOMC) mesoporous carbon [100], OMCs have been extensively used as catalyst support materials for fuel cells [140,142-146], The large surface area and 3D connected monodis-persed mesospheres facilitate diffusion of the reactants, making them very attractive materials as catalyst supports [100]. 

In the present paper, we will focus in a first step, on the results obtained using the same parent support (silica gel) modified by alkyl-dimethyl chlorosilanes of various alkyl chain length 1, 4, 8 and 18 carbon atoms. This material presents a disordered mesoporous texture [8]. 

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. 

Nanoporous SiC-based materials are difficult to obtain due to the high formation temperature. Disordered nanoporous silicon carbide ceramics can be fabricated by a solid-gas reaction of ordered mesoporous carbon replica with silicon vapor [82], and a chemical vapor infiltration of dimethyldichlorosilane inside mesoporous silica following by the removal of silica [83]. Recently, highly ordered mesoporous SiC materials with uniform pore sizes and ultralarge surface areas have been synthesized by fully impregnating polycarbosilane... 

Pahner, J.C. and Gnhhins, K.E. 2012. Atomistic models for disordered nanoporous carbons nsing reactive force fields. Micropor. Mesopor. Mater. 154 24—37. 

Fuertes and Nevskaia [139] developed a vapor deposition polymerization (VDP) method to prepare OMCs. Carbon precursor FA was infiltrated into the pores via vapor-phase adsorption at room temperature. When ordered SBA-15 silica was used as a template, the resultant carbon possessed a unimodal pore structure similar to that of CMK-3. However, when a disordered mesoporous silica was used as a template, mesoporous carbon with a well-defined bimodal pore system (mesopores centered at 3 and 12 nm) was obtained, as can be seen from Figure 2.19. A mechanism responsible for the formation of such carbons was subsequently proposed [140] based on the degree of carbon infiltration, which can be controlled with the VDP method. Kruk et al. [141] described a polymerization method for carbon infiltration, which was believed to ensure uniform filling [142] and avoid the formation of nontemplated carbon. 

Mesoporous ZSM-5-S and ZSM-5-M samples prepared by using ordered mesoporous carbon (CMK-3) and disordered carbon rods (C-MCM l) as the hard template, respectively, were compared with the conventional ZSM-5-C in methane aromatization [67] The Mo-ZSM-5-S and Mo-ZSM-5-M catalysts showed similar conversions of methane, but higher yields of aromatics compared with Mo-ZSM-5-C. The mesoporous catalysts were also more stable than Mo-ZSM-5-C. The formation of the secondary mesoporous system within the zeoUte crystal, which may lead to easier access to the active sites for reactants and be favorable for the diffusion of larger molecules formed in the microporous channels during the methane aromatization reaction, account for the better stability of the mesoporous systems. 

Group 1. - 7Li NMR spectroscopy was used to characterise a lithium/ graphite intercalation compound with a formula close to LiC 1 In situ solid-state 7Li NMR data were reported for lithium inserted into disordered carbon. There was evidence for both Lis+ and metallic lithium species.2 7Li and 13C solid-state NMR spectra were used to characterise a mesoporous tantalum oxide lithium fulleride (Ceo) composite material.3... 

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