Catalytic dehydration of fructose to 5-hydroxymethylfurfural over Nb2O5 catalyst in organic solvent

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in DMSO was performed over Nb2O5 derived from calcination of niobic acid at various temperatures (300-700 degrees C). The catalysts were characterized by powder X-ray diffraction, N-2 physical adsorption, temperature-programed desorption of NH3, n-butylamine titration using Hammett indicators, infrared spectroscopy of adsorbed pyridine, and X-ray photoelectron spectroscopy. It was found that both catalytic activity and surface acid sites decrease with increasing calcination temperatures. The Nb2O5 derived from calcination of niobic acid at 400 degrees C reveals the maximum yield of HMF among all the catalysts, although the amount of acid sites on the catalyst is lower than that on the sample calcined at 300 degrees C. The results suggest that the presence of larger amounts of strong acid sites on the surface of the Nb2O5 calcined at 300 degrees C may promote side reactions. The Nb2O5 prepared at 400 degrees C shows 100% fructose conversion with 86.2% HMF yield in DMSO at 120 degrees C after 2 h. The activity of the catalyst decreases gradually during recycle because of coke deposition; however, it can be fully recovered by calcination at 400 degrees C for 2 h, suggesting that this catalyst is of significance for practical applications. (C) 2012 Elsevier Ltd. All rights reserved.