Engineering Cooperative Acid Sites in Hydroxyapatite via Surface Fluorination for Selective Conversion of Glucose to...

The efficient conversion of glucose to 5-hydroxymethylfurfural (HMF) is a critical step toward the sustainable production of biomass-derived platform chemicals; however, achieving high selectivity in water using robust heterogeneous catalysts remains challenging. In this study, surface-fluorinated hydroxyapatite catalysts enable the selective transformation of glucose to HMF via tunable acid functionality. Surface fluorination is proposed to induce electronic polarization within the apatite lattice, which may increase the Lewis acidity of exposed Ca²⁺ centers while simultaneously generating Brønsted acidic hydroxyl species. The comprehensive physicochemical characterization using X-ray diffraction (XRD), Raman spectroscopy, solid-state ¹⁹F and ³¹P magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and transmission electron microscopy (TEM) revealed that fluorination predominantly modifies the catalyst's surface without disrupting the apatite framework, leading to the formation of cooperative Lewis-Brønsted acid sites. Among the prepared catalysts, FH5 (5 wt% fluorinated HAP) exhibits the optimal balance of acidity, achieving an HMF yield of 55.3% and a high selectivity of 71.3% under optimized conditions. The catalyst further demonstrates excellent structural stability and recyclability over 10 cycles. This study demonstrates that surface fluorination effectively tailors acid functionality in hydroxyapatite, offering new insights for the rational design of heterogeneous catalysts for selective biomass conversion in green media.