Impact of activation on properties of carbon-based solid acid catalysts for the hydrothermal conversion of xylose and hemicelluloses

Activation plays an important role in improving the pore structure of the carbon materials preparation. For carbon-based solid catalysts, activation could provide the high specific surface area and porosity. In this work, non-activated, KOH-activated, ZnCl2-activated treatments were comparatively discussed to prepare carbon-based solid acid catalysts for furfural production from xylose and hemicelluloses. These prepared catalysts were characterized by SEM, FT-IR, elemental analysis, Raman, N-2 adsorption-desorption and Boehm titration. The results showed that the chemical activated treatment could significantly improve the specific surface area of carbon-based solid catalysts, but also had an important influence on the distribution of surface functional groups especially for decreasing of the -SO3H density and the enhancement of the phenolic -OH and -COOH density. For the highest -SO3H density of non-activated carbon-based catalyst, it displayed higher catalytic activity in the conversion of xylose to furfural than other catalysts. Meanwhile, using non-activated carbon-based catalyst in the aqueous solution, the maximum furfural yield of 50% was obtained from hemicelluloses at 200 degrees C for 2.5 h, the maximum xylose yield of 55% was achieved at 200 degrees C for 1.5 h. While KOH-activated carbon-based catalyst exhibited the excellent catalytic performance to produce xylooligosaccharide with the highest yield of 62% at 180 degrees C for 1.5 h.