The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for 'biodiesel' production.

Carbonization of d-glucose at 573−723 K followed by sulfonation produces a functionalized amorphous carbon material with acid catalytic activity as a solid-acid replacement for sulfuric acid. The carbon material contains phenolic hydroxyl, carboxylic acid, and sulfonic acid groups and exhibits high catalytic performance for liquid-phase acid-catalyzed reactions. Carbonization at higher temperature followed by sulfonation also results in amorphous carbon, but the resultant does not exhibit catalytic activity although the amorphous carbon has sufficient amount of sulfonic acid groups. Structural and active site analyses suggest that the marked difference in catalytic activity is due to the accessibility of reactants to sulfonic acid groups in the carbon structure.

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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Two-dimensional metal oxide sheets in HTiNbO(5) and HSr(2)Nb(3)O(10), cation-exchangeable layered metal oxides, were examined as solid acid catalysts. Exfoliation of HTiNbO(5) and HSr(2)Nb(3)O(10) in aqueous solutions formed colloidal single-crystal TiNbO(5)(-) and Sr(2)Nb(3)O(10)(-) nanosheets, which precipitated under an acidic condition to form aggregates of HTiNbO(5) nanosheets and HSr(2)Nb(3)O(10) nanosheets. Although esterification of acetic acid, cracking of cumene, and dehydration of 2-propanol were not catalyzed by original HTiNbO(5) because of the narrow interlayer distance, which prevents the insertion of organic molecules, HTiNbO(5) nanosheets functioned as a strong solid acid catalyst for the reactions. Nanosheets of HSr(2)Nb(3)O(10) exhibited no or slight catalytic activity for these reactions. NH(3) temperature-programmed desorption and (1)H magic-angle spinning nuclear magnetic resonance spectroscopy revealed that HTiNbO(5) nanosheets have strong Brønsted acid sites, whereas HSr(2)Nb(3)O(10) nanosheets do not.

5-Hydroxymethylfurfural (HMF), one of the most important intermediates derived from biomass, was directly produced from monosaccharides (fructose and glucose) and disaccharides (sucrose and cellobiose) by a simple one-pot reaction including hydrolysis, isomerization and dehydration using solid acid and base catalysts under mild conditions.

2,5-Diformylfuran (DFF) was selectively synthesized from 5-hydroxymethylfurfural using a hydrotalcite-supported ruthenium catalyst (Ru/HT) by oxidation with molecular oxygen under mild reaction conditions. A combination of hydrotalcite, Amberlyst-15, and Ru/HT catalysts successfully afforded direct synthesis of DFF from hexoses such as fructose and glucose via isomerization, dehydration, and successive selective oxidation in one pot. Stepwise addition of catalyst improved DFF yield up to 49% from fructose and 25% from glucose, respectively.

This review is intended to introduce recent progress in the characterization, synthesis and catalysis of hydrotalcite (HT) and HT-related materials. NMR, in situ neutron diffraction and TG-DTA techniques have been used to determine the local structure and structural changes of HT. Various synthetic methods of controlling the morphology of HT are introduced together with the crystal formation mechanism. The preparation methods of magnetic HTs are also included. The HT acts as a heterogeneous base catalyst for efficient transformations of organic compounds such as the synthesis of glycerol carbonate, transesterification of oils (biodiesel production) and carbon-carbon bond formations. The HT has also been used as a support for immobilizing various metal species (Ru, Pd, Ag, Au, Pt, Cu, V, Mn etc.), which enables highly selective organic reactions such as dehydrogenation of alcohols and deoxygenation of epoxides. Cooperative actions between basic sites of the HT surface and supported metal species are introduced. It is also shown that the HT can work together with other solid acids and metal catalysts to promote sequential reactions in a one-pot manner, which gives us a very important methodology for environmentallybenign synthesis of value-added chemicals, especially from biomass-derived compounds.