A remarkable bifunctional carbon-based solid acid catalyst derived from waste bio-tar for efficient synthesis of 5-hydroxymethylfurfural from glucose

The conversion of abundant and inexpensive glucose to 5-hydroxymethylfurfural (HMF) is a critical step in the roadmap towards renewable biomass resources for production of fuel and key chemicals instead of fossil resource. A low-cost bifunctional solid acid catalyst capable of both isomerization and dehydration processes is essential for the success of this reaction route. To this end, in this paper, we present a novel porous carbon-based solid acid catalyst derived from bio-tar, functionalized by sulfonation and Al-Ti metal loading with structural regulation. We systematically investigated the influencing factors including reaction temperature, time, catalysts loading amount, and type of solvent during isomerization of glucose and the subsequent dehydration reactions. The synthesized catalyst (Al-Ti/SAPC) exhibited outstanding catalytic performance, converting 96.1% of glucose to 74.6% HMF under optimum conditions (140℃, 4 h, DMAO: H₂O = 4:1, and 20 wt% NaCl). The cooperation of two types of acid sites was the primary contributor to this exceptional catalytic activity of Al-Ti/SAPC. When the ratio of DMSO to H₂O was adjusted to 4:1, the problem of poor HMF selectivity in a single solvent could be significantly improved, and the hazard caused by excessive water in the system for glucose conversion could also be avoided. Additionally, a detailed kinetic model was developed to further elucidate the specific roles of the decorated acid sites during catalytic conversion of glucose. Overall, we established a highly cost-effective and efficient heterogeneous catalytic system for directed HMF production and provided a high-added approach to biomass waste for promising sustainable biomass utilization.