Catalytic conversion of cellulose to reducing sugars over clay-based solid acid catalyst supported nanosized SO42--ZrO2

Cellulose is the most abundant form of biomass on earth, and is considered as an alternative for fuels and chemicals. The hydrolysis of cellulose to platform compounds, such as reducing sugars (RS), is one of the most important ways for the utilization of cellulose. In this study, the solid acid catalysts of SO42--ZrO2/montmorillonite (SZ-Mt) were prepared by coupling SO42- with ZrO2 and then introducing into the interlayer of Mt using the coprecipitation method. Meanwhile, the catalytic performance of the SZ-Mt catalysts for the hydrolysis of cellulose to RS in water was studied. The catalysts were characterized by XRD, FT-IR, BET, SEM(EDS), NH3-TPD and XPS. The catalytic results showed that the SZ-Mt composite calcined at 500 degrees C with the molar ratio of S/Zr of 0.3 showed the highest total reducing sugars yield of 30.1%. The characterization results revealed that the surface SO bonds of sulfated zirconium oxide could gradually change from O=S-OH groups (type I, -HSO4) to O = S = O groups (type II, -S2O7). It was concluded that the surface S-OH groups in type I were responsible for the hydrolysis of cellulose in the low molar ratio of S/Zr and the new S-OH bonds formed by breaking the S-O-S bonds in type II were contributed to the conversion of cellulose in the high molar ratio of S/Zr. Finally, the mechanism of cellulose hydrolysis on the SZ composites was suggested.