Unraveling the hydrolysis of β-1,4-glycosidic bond in cello-oligosaccharides over carbon catalysts

Carbon catalysts having weakly acidic groups are uniquely active for hydrolysis of cellulose to produce cello-oligosaccharides and glucose. Although adsorption of cellulose molecules on carbon is attributed as the cause for this behavior, the effect of adsorption on the reaction is not well understood. In order to understand the underlying mechanism, we investigated the hydrolysis of cello-oligosaccharides with varying chain length over different catalyst. Carbon catalysts favored hydrolysis of larger oligosaccharides with an 11-fold increase in reaction rate constant from cellobiose to cellohexaose. Activation energy required to cleave the glycosidic bonds reduced concurrently with increase in molecule size. Based on these data, in conjugation with the stronger affinity of adsorption for larger oligosaccharides, we propose that axial adsorption within the micropores of carbon causes conformational change in the structure of cello-oligosaccharide molecules, resulting in reduction of activation energy required to cleave the β-1,4-glycosidic bonds. Consequently, this translates to higher rate of reaction for larger cello-oligosaccharides and explains the high reactivity of carbon catalyst towards cellulose hydrolysis.