Kaolinite: A natural and stable catalyst for depolymerization of cellulose to reducing sugars in water.

Kaolinite, a natural, abundant, low cost, and eco-friendly material, has been widely used as filler, additives, adsorbent and coatings. In the study, kaolinite was evaluated for the performance of the hydrolysis of cellulose in water. The effects of mass ratio, reaction temperature, reaction time and water amount were investigated in a batch reactor. The fresh and regenerated catalysts were characterized by XRD, FT-IR and TG-DTG. The catalytic results showed that the highest TRS yield of 38.8% was obtained on the kaolinite at 200 °C with the mass ratio of catalyst to cellulose of 0.2 for 3 h. Moreover, kaolinite was a stable catalyst after regeneration and the yield of TRS decreased from 38.8% to 38.1% after five times reuse. Kaolinite contains abundant surface Al-OH groups, and the high TRS yield for kaolinite should be attributed to the H+ ions released from the surface OH groups. This work provides a promising strategy for efficient cellulose hydrolysis into fine chemicals by natural clay minerals. Unlabelled Image • Kaolinite is an efficient catalyst for the hydrolysis of cellulose in water. • Kaolinite presents a high regeneration stability. • Surface Al-OH groups are responsible for the cellulose hydrolysis. • H-bond between Al-OH and Si O weakens the O H bond in Al-OH groups. • H+ ions in Al-OH groups are responsible for the depolymerization of cellulose. [ABSTRACT FROM AUTHOR]