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.