High efficient production of 5-hydroxymethyl-furfural from glucose over AACH @ γ-AlOOH catalyst: Insights into structure, acidic properties and performance

A easy-to-handle and bi-functional solid water-tolerant catalyst with the balance of Brønsted acid site ( BAS) and Lewis acid site (LAS) is crucial for the efficient conversion of glucose into 5-hydroxymethylfurfural (HMF). In the work, the AACH@γ-AlOOH (designated as N_y@γ-AlOOH) catalysts were synthesized through the in-situ AACH substitution of γ-AlOOH, where the AlO₆ octahedral units served as the wate - tolerant LAS with mild acid strength, while the unsaturated AlO₅ pentahedral units acted as the weak BAS, together forming Lewis - Brønsted acid pairs at molecular- level proximity. Glucose turnover and HMF selectivity were enhanced due to the rapid fructose transfer from LAS to the adjacent BAS for its dehydration to HMF, facilitating LAS liberation for another glucose turnover. Under an optimized catalyst N_4/11@γ-AlOOH, a high HMF yield of 73.8 % was obtained in biphasic system of 1-butanol / H₂O - NaCl (20 wt%) at 140 °C for 3 h.