Organically Functionalized Mesoporous Silica Network for One-Pot Synthesis of 5-Hydroxymethylfurfural from Glucose in Water

Abstract

The conversion of lignocellulosic biomass to 5-hydroxymethylfurfural (HMF), a key renewable molecule and a potential alternative to petroleum-based chemicals, is of great research interest. In this study, we prepared a t-SiO₂@B@A catalyst consisting of a mesoporous silica support, where surface −OH groups were grafted with 3-(aminopropyl)triethoxysilane (APTES), followed by functionalization with 4-formylbenzoic acid. The synthesized t-SiO₂@B@A catalyst, bearing Brønsted basic (─C═N─) and acidic (−COOH) sites, exhibited bifunctional activity for the selective production of HMF from glucose in water. The structural and chemical properties of the t-SiO₂@B@A catalyst were determined using various characterization techniques, such as XRD, BET, FESEM, TGA, FTIR, TPD-NH₃/CO₂, and solid-state cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR) spectroscopy, which confirmed the successful incorporation of organic moieties onto the silica support. The mesoporosity of the silica support was well maintained after surface modification, exhibiting a surface area of 266.4 m²/g, with a total acidity of 2.27 mmol/g and thermal stability up to 400 °C. The reaction system was optimized with various parameters, such as temperature, reaction time, catalyst amount, and solvents. Consequently, an HMF yield of 69.7% was achieved after 6 h at 120 °C over the t-SiO₂@B@A (0.5 w/v %) catalyst. Moreover, the catalyst showed good recyclability for eight test cycles without significant loss of catalytic activity. A kinetic model was developed to monitor the conversion of glucose and the temperature dependence of HMF production. Based on numerical modeling, the first step, isomerization of glucose to fructose, was found to be slower (rate constant: k_B1 = 0.348 min^–1) while the second step, dehydration of fructose to HMF is faster (rate constant: k_B1 = 0.348 min^–1). This study provides an efficient and environmentally benign method for the conversion of glucose to HMF, highlighting its potential for industrial applications.