Solid acids are conventional materials that have wide applications in chemical production, separation/purification, and polymer-electrolyte fuel-cell (PEFC) technologies, and the chemical industry is currently searching for a highly active and stable solid acid to improve the environmental safety of the production of chemicals and energy. Over 15 million tons of sulfuric acid is annually consumed as "an unrecyclable catalyst"-which requires costly and inefficient separation of the catalyst from homogeneous reaction mixtures-for the production of industrially important chemicals, thus resulting in a huge waste of energy and large amounts of waste products. The "green" approach to chemical processes has stimulated the use of recyclable strong solid acids as replacements for such unrecyclable "liquid acid" catalysts. [1][2][3][4] Thermostable strong solid acids would have genuine applications in PEFCs as proton conductors, for improving fuel efficiency, and for reducing the use of noble-metal catalysts by increasing the working temperature.[5] However, a major obstacle to such progress is the lack of a solid acid that is as active, stable, and inexpensive as sulfuric acid.An ideal solid material for the applications considered here should have high stability and numerous strong protonic acid sites. It is essential for the solid acid to maintain strong acidity even in water since water participates in fuel-cell reactions and many industrially important acid-catalyzed reactions. While organic acid/inorganic solid oxide hybrids and strong acidic cation-exchangeable resins, including perfluorosulfonated ionomers (for example, nafion), have been studied extensively as promising approaches for the construction of desired solid acids or proton conductors, [6] such materials are expensive and the acid activities are still much lower than that of sulfuric acid.[3] These drawbacks have limited their practical utility. Herein, we report the synthesis of a carbon-based solid acid with a high density of sulfonic acid groups (SO 3 H) and discuss its performance as a novel strong and stable solid acid. Here, a new strategy is adopted for the development of new types of solid acid: a carbon material is obtained by incomplete carbonization of sulfoaromatic hydrocarbons and consists of small polycyclic aromatic carbon sheets with attached SO 3 H groups. This approach is simple and allows for the use of sulfoaromatic hydrocarbons-strong, stable solvent-soluble acids (for example, benzene sulfonic acid and naphthalene sulfonic acid)-as insoluble solid acids.Such carbon-based solid acids can be readily prepared by heating aromatic compounds such as naphthalene in sulfuric acid at 473-573 K. [7] In this synthesis, the sulfonation of the aromatic compounds is the first stage of the reaction. The resulting sulfonated aromatic compounds are incompletely carbonized, which results in the formation of a solid with a nominal sample composition of CH 0.35 O 0.35 S 0.14 . The total yield of the product based on carbon is about 55 % by this metho...

HTiNbO 5 , HTi 2 NbO 7 , and HTiTaO 5 nanosheets obtained by exfoliation of protonated cation-exchangeable layered metal oxides are examined as solid acids. These nanosheets exhibit high catalytic activity for esterification of acetic acid and hydrolysis of ethyl acetate, competing with niobic acid, Nb 2 O 5 ‚nH 2 O. NH 3 temperature-programmed desorption reveals that the acidity of the nanosheets corresponds to the density of strong acid sites of H-ZSM-5 or niobic acid. 1 H magic-angle-spinning nuclear magnetic resonance spectroscopy suggests that bridging hydroxyl groups (Ti(OH)M) (M ) Nb 5+ or Ta 5+ )) on these titanium niobate/tantalate nanosheets function as strong Brønsted acid sites that are available for this reaction.

Solid acids are conventional materials that have wide applications in chemical production, separation/purification, and polymer-electrolyte fuel-cell (PEFC) technologies, and the chemical industry is currently searching for a highly active and stable solid acid to improve the environmental safety of the production of chemicals and energy. Over 15 million tons of sulfuric acid is annually consumed as "an unrecyclable catalyst"-which requires costly and inefficient separation of the catalyst from homogeneous reaction mixtures-for the production of industrially important chemicals, thus resulting in a huge waste of energy and large amounts of waste products. The "green" approach to chemical processes has stimulated the use of recyclable strong solid acids as replacements for such unrecyclable "liquid acid" catalysts. [1][2][3][4] Thermostable strong solid acids would have genuine applications in PEFCs as proton conductors, for improving fuel efficiency, and for reducing the use of noble-metal catalysts by increasing the working temperature.[5] However, a major obstacle to such progress is the lack of a solid acid that is as active, stable, and inexpensive as sulfuric acid.An ideal solid material for the applications considered here should have high stability and numerous strong protonic acid sites. It is essential for the solid acid to maintain strong acidity even in water since water participates in fuel-cell reactions and many industrially important acid-catalyzed reactions. While organic acid/inorganic solid oxide hybrids and strong acidic cation-exchangeable resins, including perfluorosulfonated ionomers (for example, nafion), have been studied extensively as promising approaches for the construction of desired solid acids or proton conductors, [6] such materials are expensive and the acid activities are still much lower than that of sulfuric acid.[3] These drawbacks have limited their practical utility. Herein, we report the synthesis of a carbon-based solid acid with a high density of sulfonic acid groups (SO 3 H) and discuss its performance as a novel strong and stable solid acid. Here, a new strategy is adopted for the development of new types of solid acid: a carbon material is obtained by incomplete carbonization of sulfoaromatic hydrocarbons and consists of small polycyclic aromatic carbon sheets with attached SO 3 H groups. This approach is simple and allows for the use of sulfoaromatic hydrocarbons-strong, stable solvent-soluble acids (for example, benzene sulfonic acid and naphthalene sulfonic acid)-as insoluble solid acids.Such carbon-based solid acids can be readily prepared by heating aromatic compounds such as naphthalene in sulfuric acid at 473-573 K. [7] In this synthesis, the sulfonation of the aromatic compounds is the first stage of the reaction. The resulting sulfonated aromatic compounds are incompletely carbonized, which results in the formation of a solid with a nominal sample composition of CH 0.35 O 0.35 S 0.14 . The total yield of the product based on carbon is about 55 % by this metho...

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