Heterogeneous Nb-containing catalyst/N,N-dimethylacetamide–salt mixtures: novel and efficient catalytic systems for the dehydration of fructose

Abstract

The development of efficient catalytic systems for the dehydration of carbohydrates to produce 5-hydroxymethylfurfural (HMF) is a very attractive topic. In this work, we synthesized a novel Nb-containing catalyst by the reaction of niobium chloride and nitrilotris(methylenephosphonic acid) (NTMPA), denoted as Nb–NTMPA. The synthesized Nb–NTMPA was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption, and Fourier transform infrared spectroscopy and used as the heterogeneous catalyst for the dehydration of fructose into HMF using the mixture of N,N-dimethylacetamide (DMA) and salts as the reaction solvent. It was found that Nb–NTMPA was very active for the reaction and a HMF yield of 85.6% could be achieved in a DMA–NaBr mixture under the optimal reaction conditions. Further study indicated that the salts could affect the activity of the reaction systems by the formation of DMA·M⁺ (M = Li, Na and K) macrocations and weakly ion-paired halide ions. Moreover, Nb–NTMPA/DMA–salt systems could also be used in the production of HMF from inulin and sucrose with satisfactory yields.