Water-induced regeneration of active acid sites in Al-MCM-41-SO₄ during continuous fructose dehydration

5-Hydroxymethylfurfural (HMF) serves as a crucial platform chemical for bio-based compounds, primarily derived from fructose dehydration–a reaction that relies heavily on Brønsted acid sites (BAS) within the catalyst. However, achieving efficient HMF production from biomass remains challenging due to the propensity for by-products formation and the limited stability of catalysts under reaction conditions. Despite advances in both homogeneous and heterogeneous catalysis, issues with scalability and catalyst longevity persist. To address these challenges, we introduce a mesoporous Al-MCM-41-SO₄ catalyst, featuring BAS originating from water neighboring the sulfate group. Herein, we demonstrate water-induced regeneration of the active site in Al-MCM-41-SO₄ during fructose dehydration, achieving a stable HMF yield of 83% over 72 h at 145 °C in a continuous reactor with a 10 wt% fructose feed. Ex situ analyses, including Si/Al atomic ratio changes, pyridine Fourier transform infrared spectroscopy (Py-FTIR), and ²⁷Al magic-angle spinning nuclear magnetic resonance (²⁷Al MAS NMR) spectroscopy, confirm that the BAS stability is sustained through interaction with the –SO₄ group, facilitating catalyst reactivation. These findings reveal that in situ generated water effectively promotes catalyst regeneration, providing a scalable approach for biomass compound dehydration without the need for additional catalyst regeneration processes.