Dual -functional carbon-based solid acid-induced hydrothermal conversion of biomass saccharides: catalyst rational design and kinetic analysis

The isomerization–dehydration cascade conversion on the saccharide platform is a pivotal route for biomass valorization, although it exhibits a specific reaction complexity that makes achieving an efficient conversion a highly technical challenge. The rational design of novel versatile solid acids is deemed to be the key to improving the cascade catalytic performance. In this paper, a dual-functional carbon-based solid acid catalyst (DFCSA) with tunable Brønsted/Lewis acid sites was developed for the cascade conversion of saccharides. The combined modification of H3PO4 and HNO3 on the carbon substrate contributed to the grafting of protonated moieties with a reasonably porous structure. With the aid of AlPO4, which has an orthorhombic crystal structure, the newly developed catalyst was able to achieve good performance for the subsequent hydrothermal conversion. Under optimal conditions, glucose and xylose were transformed with high product yields: 38.2 mol% levulinic acid and 69.7 mol% furfural, respectively. In addition, the catalyst displayed excellent hydrothermal stability, with only a slight degradation in activity after 10 cycles, which was ascribed mainly to the high thermal stability of AlPO4 and the firm grafting of the surface functional groups. As shown by the kinetic analysis, the DFSCA catalyst had a higher conversion rate and lower activation energy in the cascade conversion of xylose than that of glucose, leading to a better yield of furfural.