Hafnium-tin composite oxides as effective synergistic catalysts for the conversion of glucose into 5-hydroxymethylfurfural

Abstract 5-Hydroxymethylfurfural (5-HMF), an important and value-added platform chemical, has inspired increasing attention. In this study, hafnium-tin composite oxides (Sn-HfO2) were prepared by one-pot coprecipitation process and used as effective synergistic catalysts for 5-HMF synthesis from the conversion of glucose. Pyridine-FTIR results reveal that Sn-HfO2 catalysts have strong Lewis and weak Bronsted acid sites. With 0.5Sn-HfO2 as the catalyst, the highest yield of 5-HMF obtained from glucose was 75.5% with 99.5% conversion at 170 °C for 2 h in a methyl isobutyl ketone (MIBK)/water biphasic system. Furthermore, the catalytic system also possesses excellent performance in converting other carbohydrates. The catalysis mechanism for the isomerization of glucose to fructose was explored by the density functional theory (DFT) method, indicating that Lewis acidic Hf active sites and proton mediator Sn-O species synergistically catalyzed the isomerization process, effectively lowering the reaction energy barrier. The cooperative action of terminal Hf-OH and Sn-OH also facilitated the formation of 5-HMF in fructose dehydration. 0.5Sn-HfO2 could be reused for four runs without significant loss of catalytic activity. This approach provides the feasibility of composite oxides as synergistic catalysts for carbohydrate conversion to 5-HMF.