Acid-modified clays as green catalysts for the hydrolysis of hemicellulosic oligosaccharides

The hydrolysis of hemicellulosic oligosaccharides (OS) was investigated using acid-activated clays (prepared from natural Porto Santo montmorillonite clay) as catalysts. Acid activation was performed in HCl solution or with aluminium exchange. The clay catalysts were characterized by XRD, N2 adsorption isotherms, CEC, FTIR, titration of acid sites in water and adsorption of sugars and disaccharides. They were tested for the hydrolysis of a model compound, maltose, and of OS-rich liquor from rice straw fractionation. The HCl-activated clays were the most efficient catalysts for maltose hydrolysis. It was demonstrated that the hydrolysis of OS into monomer sugars over a clay catalyst is technically feasible and that this reaction leads to the selective removal of glucose, arabinose and acetic acid side groups from the OS structure, thus yielding simpler xylo-oligosaccharide chains. Furthermore, no significant conversion of monomer sugars into furans was observed