Insight into Fructose Dehydration over Lewis Acid α-Cu2P2O7 Catalyst

Key information on direct conversion of fructose into 5-hydroxymethylfurfural (5-HMF) over Lewis acid sites was investigated by combining experimental and computational studies. A series of alpha-copper pyrophosphate (alpha-Cu2P2O7) was synthesized and used as a heterogeneous catalyst model for bifunctional acid-catalyzed fructose dehydration under hot compressed water at mild temperature. Structural and phase transformations of the catalyst samples were systematically characterized by in situ X-ray absorption spectroscopy (in situ XAS), X-ray powder diffraction (XRD) and Transmission electron microscopy (TEM). The type of acidic site was verified by in situ pyridine-adsorbed Fourier-transform infrared spectroscopy (in situ Py-FTIR). Results revealed that calcination temperature greatly impacted microstructure, acid strength, and activity of the alpha-Cu2P2O7 catalysts. Lewis acid sites showed the main activity on alpha-Cu2P2O7 catalyst surfaces. Catalytic performance was strongly dependent on reaction temperature and reaction time. Under optimal reaction condition, the calcined sample at 900 degrees C exhibited the best catalytic performance with 5-HMF production yield of 42.0%. Results from density functional theory (DFT) revealed that fructose dehydration over alpha-Cu2P2O7 catalyst was enhanced by increasing reaction thermodynamics via Lewis acid sites.