Bifunctional mesoporous silica solid acids for transformation of glucose to 5-hydroxymethylfurfural

Lignocellulosic biomass is a promising renewable resource that can be converted into glucose, a precursor for the synthesis of high-value bio-chemicals, such as 5-hydroxymethylfurfural (HMF). However, the conversion of glucose to HMF using conventional liquid and solid acids is challenging due to the formation of byproducts, leading to low HMF yield. In this study, bifunctional solid acid catalysts (named Al-SA-S15) consisting of aluminum (Al) as Lewis acid sites and sulfonic acid (SA) as Brønsted acid sites were prepared by direct synthesis. The catalysts were then evaluated for the transformation of glucose to HMF using a co-solvent medium of acetone and water. Among the catalysts tested, the 5Al-15SA-S15 catalyst with a Si/Al molar ratio of 5 and a 15 mol% of sulfonic acid groups achieved 95% conversion of glucose and a 51% yield of HMF. The 5Al-15SA-S15 catalyst was found to be stable under the studied conditions, with no leaching of acidic groups observed. It could be easily regenerated by washing with acetone and reused for more than five times without significant loss of performance. This study provides a deep understanding of solid acid catalysts, with precise control of acidic nature and sites for the conversion of biomass into high-value added products.