Optimization of Glucose Dehydration to 5-Hydroxymethylfurfural over Fe3O4–SiO2/Al2O3 Catalyst Using Response Surface Methodology in a Biphasic System

Converting glucose into 5-hydroxymethylfurfural (HMF) via catalytic methods is essential for creating renewable chemicals and biofuels. Nonetheless, the process faces challenges due to by-products. This research introduces a cost-effective iron monometallic catalyst supported on silica–alumina (Fe3O4-SiO2/Al2O3), prepared by a straightforward co-precipitation technique. Its structure and active sites were extensively characterized using FTIR (Fourier transform infrared spectroscopy), TGA (thermogravimetric analysis), XRD (X-ray diffraction), SEM-EDX (Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy), XPS (X-ray photoelectron spectroscopy), NH3-TPD (Temperature-programmed desorption), and N2 adsorption–desorption (BET). Glucose dehydration was performed in a biphasic water/methyl isobutyl ketone (H2O: MIBK, 1:4, v/v) system, which facilitated in situ HMF extraction and reduced humin formation. Parameters such as temperature (170–190 °C), reaction time (10–14 h), and catalyst loading (25–75 wt%) were optimized through response surface methodology using a Box–Behnken design (RSM–BBD). The synergistic effect among Si, Al, and Fe increased the number of Lewis and Bronsted acid sites, thereby enhancing glucose isomerization to fructose and boosting HMF selectivity. Under optimal conditions (180 °C, 12 h, 50 wt% catalyst), a maximum HMF yield of 60.13% with 96.12% glucose conversion was obtained, along with a notable reduction in by-products. This yield is among the highest reported for monometallic catalysts under similar conditions. The catalyst was reused up to four times and could be regenerated, showing fair stability. Overall, this work offers a potentially scalable, more environmentally favorable method for efficient glucose conversion, underscoring the potential of bifunctional monometallic catalysts combined with biphasic systems for sustainable HMF production.