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

In this study, HMF was synthesized using homogeneous and inhomogeneous aluminum-based catalysts for the conversion of cheap fructose syrup, HFCS # 42, in NADES . The catalytic mechanism of “armour removal” occurring on the surface of alumina was revealed, which opens up the possibility of using commercial metal oxides as solid acid catalysts that can be recycled. • Homogeneous and heterogeneous aluminum-based catalysts were used as the effective catalysts for the HMF synthesis in NADES . • High yield of HMF was obtained with substrate fructose corn syrup 42 # (HFCS-42) as a cheap and abundant substrate. • A novel mechanism for the synthesis of HMF from in situ-formed aluminum-based active catalytic sites has been elucidated. 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.