Catalytic hydrolysis of cellulose to reducing sugar over acid-activated montmorillonite catalysts

The hydrolysis of cellulose to reducing sugar in water solution over a series of solid catalysts was studied, including the H-form zeolite, montmorillonite, and acid-activated montmorillonite. The acid-activated montmorillonite and the solid reaction products were characterized by using X-ray diffraction, Fourier transform-infrared spectroscopy, scanning electron microscopy and thermal analysis. The Brosted-acid sites of the acid-activated montmorillonite were determined. The optimum reaction time and temperature of hydrolysis were also investigated over acid-activated montmorillonite catalysts. Among the solid acid catalysts tested, acid-activated montmorillonite catalysts showed higher catalytic activity. The montmorillonite treated by H2SO4 had a higher conversion of cellulose up to 91.2%, while the montmorillonite treated by 10% H3PO4 showed a higher yield of reducing sugar of 16.9%. Anions adsorbed on montmorillonite increased the yield of reducing sugar and PO43- ions probably played a role in the formation of reducing sugar. The characterization results showed that acid activation had little influence on the layered structure of montmorillonite. The crystalline structure of cellulose was almost destroyed at 473 K. (C) 2012 Elsevier B.V. All rights reserved.