Hydrolysis of Cellobiose over Selective and Stable Sulfonated Activated Carbon Catalysts

Abstract

Activated carbon is functionalized by different treatments with sulfuric acid and hot liquid water and used as catalyst for the hydrolysis of cellobiose in a continuously operated fixed bed reactor. Characterization results reveal that the chemically treated materials are more disordered with a lower degree of graphitization, while adsorption isotherms demonstrate that van der Waals forces dominate the interaction between carbohydrates and the surface of catalysts. All catalysts are stable during the hydrolysis of cellobiose under flow conditions. Carbon catalysts with a limited fraction of sulfonic acid groups exhibit moderate cellobiose conversion but a higher and sustained glucose selectivity. The high selectivity is attributed to a higher fraction of weak acid sites, where degradation of glucose only occurs to a limited extent due to less accessibility and competitive adsorption with cellobiose. Furthermore, the strong sulfonic acid groups are more accessible for degradation reactions to occur. In contrast, the catalyst with a higher fraction of sulfonic acid groups shows increased cellobiose conversion but decreased glucose selectivity because glucose monomers can be converted to degradation products at these sites.