Mechanism of 5-hydroxymethylfurfural preparation from glucose by a nonmetallic Lewis/Brønsted bifunctional solid acid catalyst CNs-PF6 under photo-induction

The preparation of 5-hydroxymethylfurfural (5-HMF) from glucose is an important reaction in the field of solid acid-catalyzed biomass conversion. The reaction is usually carried out at high temperatures and pressures. In this paper, a nonmetallic solid acid catalyst CNs-PF 6 was synthesized from cheap melamine and hexafluorophosphoric acid (HPF 6 ) by low-temperature calcination and immersion method. The catalyst achieved the conversion of glucose to 5-HMF by photo-induction at a lower temperature (80 °C) and atmospheric pressure. And it also has a very high stability for recycling. The unique mechanism of photo-induced CNs-PF 6 catalyzing the conversion of glucose to 5-HMF has been elucidated by photoelectron characterization, transient absorption spectroscopy and theoretical calculations. Namely, under photoinduction, CNs-PF 6 possesses both Lewis acid and Brønsted acid properties. Since light simultaneously provides energy for the conversion reaction, it enables the reaction to proceed at lower temperatures and pressures. Combining light induction with acid catalysis fully leverages the synergistic effects between photocatalysts and solid acid catalysts. This research provides a new successful model for achieving biomass conversion at lower temperatures and pressures. The Mechanism for Acid/Photocatalysis Synergistically Catalyzed Glucose Conversion to 5-Hydroxymethylfurfural • Photo-induced conversion of glucose to 5-HMF at lower temperature and pressure. • Separation of photogenerated carriers endows CNs-PF 6 Lewis/Bronsted acid properties. • CNs-PF 6 catalyzed glucose's isomerization with its Lewis acid property under light. • CNs-PF 6 catalyzed fructose converting to 5-HMF with its Bronsted acid properties.