The reaction mechanism of the hydrolysis of cellulose by a carbon-based solid acid, amorphous carbon
containing graphene sheets bearing SO3H, COOH, and phenolic OH groups, has been investigated in detail
through the hydrolysis of water-soluble β-1,4-glucan. Whereas a range of solid strong Brønsted acid catalysts
(inorganic oxides with acidic OH groups, SO3H-bearing resins, and the carbon-based solid acid) can hydrolyze
the β-1,4-glycosidic bonds in cellobiose (the shortest water-soluble β-1,4-glucan), the tested solid acids except for
the carbon material, consisting of conventional solid acids, cannot function as effective catalysts for the
hydrolysis of cellohexaose (a long-chain water-soluble β-1,4-glucan). However, the carbon material exhibits
remarkable catalytic performance for the hydrolysis of cellohexaose: the turnover frequency (TOF) of SO3H
groups in the carbon material exceeds ca. 20 times those of the conventional solid acids, reaching that of sulfuric
acid, which is the most active catalyst. Experimental results revealed that inorganic oxides with acidicOHgroups
are not acidic enough to decompose the hydrogen and β-1,4-glycosidic bonds in cellohexaose molecules
aggregated by strong hydrogen bonds as well as cellulose and that the SO3H groups of the resins that do not
adsorb β-1,4-glucan are unable to attack the hydrogen and β-1,4-glycosidic bonds in cellohexaose molecules
effectively. In contrast, the carbon material is capable of adsorbing β-1,4-glucan by phenolic OH or COOH
groups in the carbon material, and SO3H groups bonded to the carbon therefore function as effective active sites
for both decomposing the hydrogen bonds and hydrolyzing the β-1,4-glycosidic bonds in the adsorbed longchain
water-soluble β-1,4-glucan aggregate. These results suggest that the synergetic combination of high
densities of the functional groups bonded to amorphous carbon causes the efficient hydrolysis of β-1,4-glucan,
including cellulose, on the carbon material.
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