Efficient synthesis of 5-hydroxymethylfurfural from high fructose corn syrup 42# (HFCS-42) in natural deep eutectic solvents (NADES) with aluminum-based catalysts, processes and mechanism

The conversion of biomass feedstock to synthesize 5-hydroxymethylfurfural (HMF) is critical for advancing biorefinery. However, direct and efficient achieving HMF from industrial raw materials remains challenging. This study developed a natural deep eutectic solvent (NADES) system using high fructose corn syrup 42 # (HFCS-42) and choline chloride (ChCl) for HMF synthesis. The performance of aluminum-based homogeneous (AlCl 3 ·6H 2 O) and heterogeneous (γ-Al 2 O 3 ) catalysts was compared within this reaction system, with high HMF yields of 55.3% and 60.9% were obtained using AlCl 3 ·6H 2 O and γ-Al 2 O 3 as catalysts, respectively. Notably, recycled γ-Al 2 O 3 demonstrated enhanced catalytic performance, achieving a 63.9% HMF yield. Systematic characterizations and density functional theory (DFT) calculations revealed that the presence of extremely low concentrations of HCl promoted the exposure of Lewis acid sites on γ-Al 2 O 3 , leading to improved catalytic activity. This study proposes a sustainable and cost-effective method for enhancing HMF synthesis from industrially acceptable HFCS-42, offering significant potential for biorefinery applications.