Sulfonated mesoporous carbon and silica-carbon nanocomposites for biomass conversion

Sulfonated mesoporous carbon or silica-carbon nanocomposite materials possess a large amount of accessible SO3H acid groups, which may have versatile applications as solid acid catalysts in biomass conversion. The mesopores can facilitate the transportation of the large biomass substrates and the targeted products. The hydrophobicity of carbon ensures the hydrothermal stability of the materials, which is essential since biomass conversion usually occurs in polar circumstances (e.g., in water), and it can facilitate the adsorption of reactants and the desorption of formed H2O during the conversion simultaneously. The other weak acid groups of carbon, like phenolic OH and COOH groups may help the adsorption of reactants or even exert a synergistic catalytic function. With the co-existence of silica phase, the mesopores can be maintained under harsh conditions, e.g., during the sulfonation synthesis step in concentrated H2SO4 at a high temperature. Furthermore, the hybrid silica-carbon surface can provide specific polarity from the synergy of both kinds of components and offer potentiality for multi-functionalization. Herein, the synthesis and fabrication of such sulfonated mesoporous carbon and silica-carbon nanocomposite wherein C-SO3H is confined in mesoporous channels is reviewed. Their state-of-the-art use in catalytic biomass-related conversion such as fatty acids esterification, carbohydrates conversion and furan-derivative condensation, are discussed in detail. The stability issues of the sulfonated carbon or silica-carbon nanocomposites for the specific catalytic reactions are specifically addressed. Finally, a general conclusion is drawn from the above and a future outlook for this class of upcoming materials in terms of synthetic challenges and catalytic application is presented.