One-pot synthesis of 5-hydroxymethylfurfural from cellobiose and sucrose using niobium-modified montmorillonite catalysts

The synthesis of platform chemical 5-hydroxymethylfurfural (5-HMF) provides favorable and efficient paths for the utilization of renewable biomass resources. In this work, highly active niobium-modified montmorillonite (Nb-Mont) catalysts were synthesized by a facile and ion-exchange method and were used for the one-pot conversion of cellobiose and sucrose to 5-HMF with optimal results. 5-HMF yield of 68.6% was obtained from cellobiose in a methyl isobutyl ketone (MIBK)/saturated salt water (SSW) biphasic solvent at 170 °C after 3 h. With sucrose as substrate in DMSO at 140 °C after 2 h, 5-HMF yield was 65.4%. The presence of Lewis and Brønsted acid sites on Nb-Mont facilitate the hydrolysis of cellobiose and sucrose and play essential roles in the subsequent isomerization of glucose monomer and the dehydration of fructose monomer. A possible reaction mechanism was proposed for the transformation of cellobiose and sucrose into 5-HMF, and the isomerization process of glucose monomer was the most critical step, confirmed by density functional theory (DFT) calculations. [NbO(OH) 2 ] + species as active sites could effectively reduce the activation energy of the isomerization process, which accelerated the synergetic proton transfer process. Nb-Mont was recycled at least four times without a prominent loss in the catalytic activity. In this study, a promising catalytic strategy was provided for heterogeneous Nb containing catalysts used in the effective synthesis of 5-HMF from carbohydrates.